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367
368

Math Teacher Fail. (i.imgur.com)

submitted ago by HanSkywalker

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[–]emceelokey 39 points40 points ago

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Here's how you fix this question.

If it takes Sarah 10 minutes to cut down one tree. If she works just as hard, how long will it take Sarah to cut down 3 trees?

You're timing the cut, not the pieces that the cut produces. Someone needs to confront that teacher about this. Nobody learned anything from that and the kid was right but got punished for being right.

[–]Slime0 11 points12 points ago

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But I think the point of the question is to remind students that a word problem is not the same as an arithmetic problem. You must consider the context when you consider a word problem. This is an important skill to learn as you start applying math to real life.

[–]voetsjoeba 3 points4 points ago

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From personal experience, this is almost never the case. When I was in high school, I used to get these ambiguous or poorly worded kind of questions sometimes. When I asked how I was meant to interpret them, the teacher generally

a) hadn't thought about that

b) told me that it's obvious and I should quit being annoying and just solve the problem

I suppose that's why I'm now a CS student.

[–][deleted] 6 points7 points ago

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you apply math to real life? never seen this one on my taxes.

[–]lyktstolpe 17 points18 points ago

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It's 3 a.m. and you're sweating over your tax forms, you've been up all night but still nothing in that form 4563 makes sense (you don't recall even visiting Samoa). In a fit of rage you tear the form in half! It only takes you a second, but leaves you with a stinging paper cut. Watching a single drop of blood slowly forming on the tip of your index finger your resentment towards the sheets of paper builds.

How long will it take you to tear the next page in THREE pieces instead of just two?

[–][deleted] 4 points5 points ago

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lol the answer is tax slayer

[–][deleted] 2 points3 points ago

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http://chzmemebase.files.wordpress.com/2011/04/taxes.jpg

[–]FrabriziovonGoethe 0 points1 point ago

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Only works if you don't have international revenue then it throws a high holy fit.

[–][deleted] 0 points1 point ago

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if I have international revenue I'm getting a accountant.

[–]howardcord 2 points3 points ago

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You're obviously not an engineer...

[–][deleted] 0 points1 point ago

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hah no I am not but get this one I was aircrew in the usaf...still didnt use that much math.

[–]mapoftasmania 1 point2 points ago

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Right. This is one of a class of questions we got trained by our teacher to look for on math tests. Another one like that is: how many fence posts do you need to build a ten yard fence with the posts spaced one yard apart?

[–]clamsmasher 0 points1 point ago

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Only 11, right? Not hard if you think about counting starting with zero instead of starting with 1. I don't think zero being a number is really stressed with children. I think they learn it as a representation of nothing, such as 12 + 0 = 12 because 12 plus nothing is still 12.

[–]marishtar 1 point2 points ago

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Under what context do you pull each individual piece out of your ass?

[–]rhl6856 0 points1 point ago

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b.s. why should a world problem have anything to do with real life? do you have any idea how contrive this is? in the real world, there are many many many more considerations to take into account (friction, air resistance, to say the least).

how come when it's math, we need to 'apply it to the real world,' but if it's say, music, there is never a 'you need to learn this cord so you can do X or Y in the real world?'

[–]Slime0 0 points1 point ago

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why should a world problem have anything to do with real life?

Well, that's what word problems are. They add context and challenge you to use math to solve a problem that is not entirely abstract.

do you have any idea how contrive this is?

I do see that it is contrived. It might even be specifically designed to trick the reader. However, it teaches a valuable lesson: when you boil a problem down to arithmetic to calculate something useful, it is not enough to simply plug in the numbers; you must consider their meaning and whether you're interpreting the situation correctly. This is a problem that a lot of people, even adults, actually have.

how come when it's math, we need to 'apply it to the real world,' but if it's say, music, there is never a 'you need to learn this cord so you can do X or Y in the real world?'

Well, one reason is that math has direct applications in other fields, such as the sciences. Music tends to exist mostly for the sake of music.

Another answer is that as a society we teach music better than we teach math. When we teach music, we hand the students instruments and show them how to use them. When we teach math, we boil it down to abstract symbols and almost entirely ignore the purpose until it comes time to do some word problems.

If music were taught as nothing more than notes on a staff, we would have to separately teach how to "apply it to the real world," so that when a student finally came across an instrument they would know what to do with it.

[–]rhl6856 0 points1 point ago

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I suppose word problems are supposed to get the student to think about modelling the real world, but, again the point is to get students to understand mathematical concepts, not 'real world concepts.'

and what you are saying about the word problems teaching students to do more than 'plug in numbers' is approximating the idea of what studying and learning mathematics is about. If you haven't already, i'd encourage you to read lockhart's lament: http://www.maa.org/devlin/devlin_03_08.html

however, I think you are confused about music vs math. the point of math is not and should not be to 'apply it to the real world.' Imagine how much music would suck if that is what society made musicians focus on. Learning to play an instrument is not the 'applying your knowledge' bit, that's the part where you actually learn music.

Much like in mathematics, doing and thinking mathematics is the important part. Mathematics is the part of the process where you reason out the area of a right triangle from the length of it's sides. Not like in grade school where they give you a formula sheet and ask you to 'plug and chug.' They have just killed mathematics.

[–]selectrix 2 points3 points ago

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The question is as it should be- the teacher got fooled by the wording that was supposed to catch the student.

[–]SirZerty 2 points3 points ago

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the question doesn't need to be fixed, the teacher does. edit: Nope I'm a retard. the question is wrong. http://www.reddit.com/r/pics/comments/ilzdw/math_teacher_fail/c24uira

[–]Kernel_Forbin 1 point2 points ago

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The main thing here is that the question has a picture of a 2x4. We aren't talking about square. The cuts, no matter how long or short they made the pieces, would still be cutting through the same amount of wood. The main misunderstanding here is that it takes 1 cut to make 2 pieces... and 2 cuts to make three pieces.

[–]throw_away_31415 3 points4 points ago*

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No I disagree, you're not a retard. The question implies three identical cuts, if it did not then there are an infinite number of answers. For example you could simply take one board and make two very minor cuts in the corners, at that rate it would take less than 5 minutes, but you'd still have 3 pieces of board.

[–]infantada 9 points10 points ago

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Sorry but the implication is a second cut. 1 cut turns 1 board into two pieces. A 2nd cut will turn one of thos pieces into 2 pieces, totalling 3. 2 cuts, 3 pieces. Size of the pieces means jackshit, since it's implied that the pieces will be of equal size, thus the two cuts will be equal. If the two cuts are equal and one cut took t time to make, then working just as hard, 2 cuts will take 2t time.

That is why the teacher failed, and that is why word problems are both valuable and dreaded.

[–]throw_away_31415 0 points1 point ago*

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Sorry but..

you've misread what I've written above, we're both stating the same argument.

[–]Doombuggyman 0 points1 point ago

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It takes Sarah 10 minutes to cut down two trees. If she works just as hard, how long will it take Sarah to cut down three trees?

FTFY.

[–]strained_brain 0 points1 point ago

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She could work just as hard, but the trees may be different sizes, or different types of wood, or the first tree may fall on her and crush her. Semantics, I know...

[–]socosoldier 0 points1 point ago

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I feel that the question doesn't need fixed because the student answered it correctly.

[–]adambascle 0 points1 point ago

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"punished" is a hilarious word to use here cause it implies grades before grade 9 mean anything at all.

[–]mcpower_ 12 points13 points ago

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For the mentally challenged:

n cut(s) = n + 1 slices

2 slices, as stated, needs 1 cut, which is 10 minutes

3 slices, needs 2 cuts, which is 10 * 2, which is 20 minutes.

[–]harriswill 1 point2 points ago

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Thanks bro.

[–]strained_brain 0 points1 point ago

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Hm... I would think:

whereas: p is pieces of wood and t is time for one cut:

  • t * (p-1)
  • t * (2-1)
  • 10 * 1

  • =10

  • t * (p-1)

  • t * (3-1)

  • 10 * 2

  • =20

So, 32 pieces of wood would take:

  • t * (p-1)
  • t * (32-1)
  • 10 * 31
  • =310

[–]rhl6856 96 points97 points ago*

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I got my MS in applied math last year, and i'm getting a PhD in computer science. This is one of our biggest issues with education in America.

A teacher who clearly has no understanding of basic mathematics.

Besides the obvious issues with the statement of this question versus what the teacher was expecting as a result, there is a bigger issue here.

What do I mean? The teacher clearly means to communicate that 'cutting into two pieces takes 10 minutes.'

However, if the teacher thinks that the statement '10 = 2.' is valid logic, then they should be happy then concluding anything I can phrase as a logical proposition. Because 10 does not equal 2.

You might say, they wrote '10 = 2 pieces.' This is even worse. 10 "what" 'equals' 2 pieces? you can only equate things of a comparable type! So you are going to tell me "10 minutes = 2 pieces"? this makes no sense at all.

To get to the heart of all the confusion, all the problems with this homework problem can be fixed with a better language. for example, if T(n) was the time, in minutes, that it takes to cut a board into n pieces, then we would assert that T(2) = 10 minutes.

But now if we ask what T(3) is, we will not be able to answer the question a priori, because it depends on the relationship between T(a) and T(b), for an arbitrary a and b. for example if T(n) = 3/2(x - 2) + 10, then T(3) = 10, but T(4) = 13.

One way to interpret the problem is that the time per cut is the same, no matter how many cuts are made, or that the the rate of change of T is constant, so if T(2) = 10, then maybe T(3) = 20.

But 'she works just as fast' could also mean, that regardless of the number of cuts, she will always take 10 minutes. or that T(n) = 10 for all n.

if only our teachers taught the part of mathematics that matters, instead of destroying it...

...this is why I hated math in high school. I'm so glad that I rediscovered it in college.

lastly, I leave you all with: http://www.maa.org/devlin/devlin_03_08.html

[–]dmalice 120 points121 points ago

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AMBIGUITY

[–]throw_away_31415 25 points26 points ago

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While you highlight the questions ambiguity. The solution on the right is actually one of an infinite number of solutions.

Hence it would not be reasonable to suggest that the cuts are of differing lengths.

(That and there is a picture next to the question which also leads us to the logic of similar cuts.)

[–]effraye 7 points8 points ago

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The question doesn't explicitly say that the second board is the same size as the first. So technically the answer could range from something close to zero to infinity.

[–]drachenstern 3 points4 points ago

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Clever clever ...

[–]derekg1000 2 points3 points ago

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good try, but that isnt what the picture from the question shows. It clearly shows a slender board being cut into shorter pieces. My question is who the fuck takes 10 whole minutes to make one cut in what would seem to be a 2x4? Hell you could probably hand saw through an entire tree trunk in 10 minutes.

[–]ChaoticAgenda 18 points19 points ago

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I think Marie just needs to get back in the goddamn kitchen and leave this shit to people who know what they're doing.

[–]AeroNotix 0 points1 point ago

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Oh dear god, I think you may have just got me fired for laughing so damn hard at my 'tracker reports'.

[–]mybreathyourlung 0 points1 point ago

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This was always a problem for me in math class. I would rely solely on the things used visually in a question because I can't handle numbers in my head.

Like in geometry, instead of just using an equation to figure out the length of C when given the length of A and B, I would actually use a ruler to measure A or B, then mark on C that length, then try and figure out the rest of the length and scale up to the size used in the example.

Obviously, this never worked.

[–]ViP_Suite 0 points1 point ago

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Great way to sum up what what rhl6856 said. Thanks!

[–][deleted] 4 points5 points ago

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  1. Teacher understands math
  2. Teacher doesn't understand wood cutting.

If she counted CUTS instead of PIECES this would have all worked out.

Also, the 10=2/15=3 are perfectly fine language for that level of math. Seriously.

[–]rhl6856 0 points1 point ago

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since when does it make sense to teach people something totally wrong, at any level? I spent my first year of college math un-learning the un-truths I learned in grade school.

it is not ok.

[–]uzimonkey 13 points14 points ago

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A teacher who clearly has no understanding of basic mathematics.

This has nothing to do with basic mathematics. It doesn't even have to do with with basic arithmetic. Most likely, he's grading a huge stack of papers and just overlooked one tiny detail: that to cut a piece into two pieces, you only make one cut. It's a forgivable mistake, these problems are designed so that if you just scan for the numbers and plug them into your calculator, you'll get most of them wrong.

You might say, they wrote '10 = 2 pieces.' This is even worse. 10 "what" 'equals' 2 pieces? you can only equate things of a comparable type!

You're trolling, right? Maybe the equals sign is not completely appropriate here, but.. you're trolling, right? He most likely has under a minute to try to explain what they did wrong, and you're complaining that he used the wrong symbol? This isn't a high school algebra course taught by a teacher that completely misses the point (I think we've all been there), this is elementary school and they're still learning basic arithmetic.

He made a mistake, he had a brain fart, and you go off on this huge tangent. Sounds to me like you're just venting that you had shitty math teachers, and that has little or nothing to do with this.

[–]Figlet212 7 points8 points ago*

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The thing is, this isn't an English paper where each submission is different...every kid in the class probably had this worksheet and the teacher either wrote this problem or has the answer key. No teacher would be like "yep, 20" all the way down the line only to take the time to "correct" this one, so I assume every kid has been told the wrong answer (or been rewarded for incorrectly getting there by him/herself).

I think that the teacher probably does have a basic understanding of mathematics (lets not go overboard here) and will feel pretty dumb when this is pointed out, but I hope they at least correct their mistake in front of the class. Even teachers makes mistakes, but it is their responsibility to correct them when they become apparent.

[–]uzimonkey 0 points1 point ago

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The thing is, this isn't an English paper where each submission is different...every kid in the class probably had this worksheet and the teacher either wrote this problem or has the answer key. No teacher would be like "yep, 20" all the way down the line only to take the time to "correct" this one, so I assume every kid has been told the wrong answer (or been rewarded for incorrectly getting there by him/herself).

I said in my other comment on this post that I seem to remember the teacher getting this same problem wrong on my niece's homework, so... maybe the answer key is wrong?

[–]Figlet212 4 points5 points ago

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I had a teacher in elementary school who would give extra credit points if we caught a mistake in her work, or in any of our answer keys.

[–]frankyb89 1 point2 points ago

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Same for most of my teachers in high school. Really made us pay attention to the correction process a lot more.

[–]Peteyjay 2 points3 points ago

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But the teacher must have a qualification in math. So to of read the question you would instantly know the answer key was wrong. Also. The teacher wrote their own working down as proof as to why 20 was incorrect. So sadly, whether or not the key is wrong, the teacher is at full fault.

[–]BeefPieSoup 5 points6 points ago

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Not trolling. I completely agree with the guy - people misuse the equals sign all over the place, and it leads to needless errors. It should be treated like a word with a specific meaning that can only be used in a particular correct context, meaning that the thing on the left is equivalent to the thing on the right. Anything else IS WRONG

[–]Singulaire -1 points0 points ago

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Uhm, you do realize that in many programming language the sign '=' stands for assignment whereas equivalence is denoted by '==', don't you?

[–]BeefPieSoup 1 point2 points ago

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Yes.

[–]adambascle 4 points5 points ago

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We seem to be in the minority but that's more or less the feeling I got. Out in every other profession in the world, 10 = 2 is stating that 10 minutes equals 2 cuts, cause due to context clues, this is very fucking apparent.

People like to argue semantics to try to make bullshit they decide is important seem important to others, when the rest of the world is busy not giving a shit.

Though, without a doubt, high school everything gets blown away by college everything.

[–]TackyOnBeans 7 points8 points ago

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but it wasn't two cuts... the teacher clearly wrote 2 PIECES

you can't say that "it's very fucking apparent" when it's completely wrong.

[–]rhl6856 0 points1 point ago

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well, this is the issue, most people don't care, and thus most people don't understand what they are saying or hearing. so our schools should be teaching people the correct syntax and semantics so they can use this 'in the real world.' that's actually what matters in mathematics, not what the arithmetic actually works out to.

[–]harbo -1 points0 points ago

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This isn't semantics. These symbols are unique, you can't argue about what they mean.

[–]CD_reflected_rainbow 6 points7 points ago

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That's not true. People use symbols in all sorts of ways. Intelligent people (and I'm including kids here) can easily sort out the meaning through context.

[–][deleted] ago

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[deleted]

[–]keramos -1 points0 points ago

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Then who was := ?

[–]Peteyjay 0 points1 point ago

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Most likely, he's grading a huge stack of papers and just overlooked one tiny detail: that to cut a piece into two pieces, you only make one cut. It's a forgivable mistake.

It's not forgivable in the slightest. He would have marked everyone who gave the correct answer as incorrect. This could mean the difference between a passing grade and a fail which could have so many negative repercussions. The teacher is paid to do a job. He/she should at least read through the exam themselves first and aquatint themselves with the answers and workings.

[–]apox64928 -2 points-1 points ago

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you're trolling... right?

[–]that_makes_no_sense -1 points0 points ago

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he's not trolling, i'm trolling. and you're trolling too.

[–]Aladar_42 2 points3 points ago

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Directed by M. Night Shyamalan.

[–]Ble_h -1 points0 points ago

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This post is one big troll.

[–]that_makes_no_sense 0 points1 point ago

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no, no. this post is one big lol

ftfy

[–][deleted] -1 points0 points ago

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"==>" is what I use, I use it in essays too. I'm in BEngineering. I clearly understood what he meant by '='. Seeing as this is like primary school mathematics, you can do away with tiny mistakes in semantics, especially in a god damn marking sheet.

It's an ambiguous question, and if you think this is the cause of problems in mathematics then you completely misunderstand primary school and high school mathematical pedagogy.

Obviously I'm not replying to you, replying to Captain PhD.

[–]rhl6856 0 points1 point ago

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i'm not saying it's the cause of all problems, but it definitely contributes.

[–]SergeiKirov 1 point2 points ago

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I don't follow you in how "works just as fast" could mean she will always take 10 minutes. The word fast implies a rate, and "just as" means the same rate (i.e., x distance cut in y minutes).

[–]rhl6856 -3 points-2 points ago

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what do you mean by 'rate' and I don't agree with your deductive skills. I agree that 'just as' in this context means something like 'the same as' or 'equal to,' but I don't know that fast means rate in this context.

maybe what I suggested might better worded in english as if she works fast enough to take the same amount of time for 3 boards.. but that is irrelevant.

The teacher is still clearly wrong, and importantly is not teaching something I would call mathematics. High schools in many other countries do not 'water down' the relevant curriculum, and that is why we are having so many problems.

read the nice long article by paul lockhart for the relevant attitude.

[–]swagger_dagger 2 points3 points ago

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You keep bringing up high school when this is clearly an elementary school problem. The ability level of high school mathematics teachers is very different than that of elementary school teachers.

Besides that, I don't see how you can insult this teachers teaching abilities. You don't know the method that the teacher used to instruct his/her students (plus, the student got the answer right, so I guess the teacher didn't teach the student the wrong way to solve the problem).

We don't know that the teacher graded this. Maybe is was a classroom volunteer, maybe it was an EA, etc. (now the teacher should be grading his/her own papers, but that's another argument).

Finally, I would like to see you go into an elementary classroom and teach them function notation. I agree with you that there are many, MANY bad math teachers out there, but you're getting a little ahead of yourself.

[–]SergeiKirov 0 points1 point ago

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Well I just don't see the ambiguity with word fast - fast does not refer to a length of time by itself, unless it is with the implication that the amount of time was short relative to some other reference time period (still with the implication that this was due to a high rate of progress of whatever activity is being done). This isn't a math issue anyway, just of the semantics of the sentence itself.

Of course I agree that the teacher seems to have a pretty poor understanding of the actual math here, but that's not what I was referring to...

[–]masasuka 0 points1 point ago

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seeing as this looks like an elementary school question, the easiest way to ask it is this:

"If it takes 10 minutes to make 2 equal cuts in a piece of wood, how many minutes will it take to make 3 equal cuts"

[–]drachenstern 6 points7 points ago

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If it takes 10 minutes to make a cut in a piece of wood producing two pieces of wood, how many minutes would it take to produce three pieces of wood?

This implies without stating that two cuts should be made.

This is, fwiw, akin to what was actually asked.

[–]masasuka 0 points1 point ago

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again, they are leaving it to interpretation, this could be producing 2 pieces of wood off the main piece (eg cutting 2 1ft sections off an 8ft piece of wood, thus giving you 2 1ft pieces of wood)

With math, you can't leave things to interpretation.

[–]drachenstern -1 points0 points ago

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With math you can't leave things to interpretation, however, with simple math tests you can. The intent was spelled out IN THE PROBLEM. Because an image was given, to remove any doubt.

There is a thin wooden rod and a saw. The intent is to saw the thin wooden rod.

[–]Peteyjay 1 point2 points ago

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Damn. Ten minutes to saw through that thing. Weak carpenter.

[–]masasuka 0 points1 point ago

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sadly we can't see the rest of the picture, perhaps that picture ends just to the right, thus the picture is showing a saw cutting a piece of wood in half, as such, 20 mins is the correct answer, 1 cut = 2 pieces, 2 cuts = 3, double the work, double the time.

[–]drachenstern 0 points1 point ago

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Now you're just being an argumentative ass. Would you like me to declare you the winner?

[–]Bubbasauru -2 points-1 points ago

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In the mind of the mathemathician, that may be what is implied. In the mind of the carpenter, not so much.

[–]drachenstern 0 points1 point ago

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Seriously. Read the rest of the threads. The point is there is an image showing the cuts to be made. I don't know how much clearer a math question can be when an image is provided, except for the teacher to understand math ...

[–]sienf 0 points1 point ago

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I was reading reddit for cheap amusement and came across this topic. I came across your post and... don't get me wrong, I don't completely agree with everything you have to say, but I like where you're coming from... And, goodness knows why, I decided to read what would commonly fall prey to my "tl;dr" filter for my lunch break...

I'm still reading that article. Thank you kind sir/madam, you have just made my day :)

[–]I_deny 0 points1 point ago

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But, but 10 = 2 in binary.

[–]takinter 0 points1 point ago

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After reading that explanation, I am going with the teacher, even though they were wrong. After years away from the classroom I now remember why I despised maths.

[–]DyceFreak 0 points1 point ago

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This reminds me of a problem in highschool I had in one of my science classes. We were learning about states of matter and the question was: "If both water and steam were at the same temperature, which would burn you more if you came in contact with it for the same period of time." Having learned about states a bit the week before I wrote: Water because it is far more dense and will transfer much more heat. The answer she wanted was: Steam because it cannot change states any further to allow heat to escape away... while this somewhat made sense, I still stand by my answer, and an f' you to leading questions in high school.

[–]Tyrsyn 0 points1 point ago

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Nerd

[–]elessarjd 0 points1 point ago

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This is an elementary math problem. No need to blow this shit out of proportion. A simple; It takes 10 mins to make a cut x 2 is more than sufficient here. Being upset about the teacher not grasping that is one thing. The algebraic breakdown is big time overkill.

[–]rhl6856 0 points1 point ago

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wait wait, who is blowing what out of proportion? no pun intended :P

I think that you are missing the point. it's not about this math problem at all, or how simple something is or isn't to solve.

the point here is that what we are supposed to be teaching in math class is how to think logically. this teacher clearly has not thought logically about these simple issues, how can she possibly teach others to do the same?

I am giving 'the algebraic breakdown' to illustrate the ambiguity of the situation. I don't care what the particular problem is to solve, and I am not solving it because I actually care how long it will take marie to cut whatever into whatever.

I am interested in the problem because I want to solve a cool puzzle, and if you can't describe the rules of the puzzle to me, you haven't done your job as puzzle maker.

it's that simple.

[–]slayemin 0 points1 point ago

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I recently finished my BS in Computer Science and minored in Philosophy. I had to take Pre-Calc II four times. Then I took Calc I twice, then Calc II twice. I had a love/hate relationship with mathematics. I hated memorizing half-angle forumulas and double-angle formulas. I still don't remember them and don't quite see how they're useful. I think the most fun I had with Math was when I got side-tracked on some interesting problems. Most memorably, I remember trying to derive and calculate the positions of a comet, or writing it a short computer program to brute-force the answer out of a complicated story problem about selling shirts. It took 15 minutes to write the program, which gave the right answer, and 2 hours to work out the answer algebraicly. I completely agree with the approach to teaching Mathematics by Devlin. It should also be applied to the way Physics is taught.

[–]jlink005 3 points4 points ago*

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My HS math teacher once told us that if we had enough knowledge to answer any particular question correctly 97% of the time, and if we took a 20 question test, we would only get a 54% (failing) grade. Therefore, we have to know our stuff 100%.

54% is the chance of getting all questions correct, not the grade you'd get.

[–]goocy 1 point2 points ago

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This is only true if all 20 questions are cumulative, so that the current question depends on the previous result.

[–]CarpeKitty 5 points6 points ago

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In highschool I once got an answer right and only got half marks. When I went up and asked about it the teacher said "It said to draw a graph & a chart"

I said, no, right there is an OR not an AND. OR. OR. OR!

Her response? "Well on the marking guide I have it says and with a half mark allocated to each".

CONGRATULATIONS! Cause we all assumed that it was 'meant' to say that!

[–]marsol0x 4 points5 points ago

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That's what bothered me the most about school. Teachers who stopped thinking on their own.

[–]emceelokey 5 points6 points ago

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Fuck dude. I had to read that question 5 times just to understand it. The kid ir right though. To cut one board into 2 pieces only takes one cut. To cut the board into 3 pieces will take 2 cuts. So if one cut took 10 minutes and the bitch is working just as fast, the second cut will take another 10 minutes so 20 minutes would be the correct answer.

What a dumb question.

[–]Slime0 1 point2 points ago

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What a dumb question.

Only learning arithmetic would be dumb. Questions that force students to connect math to real life are important.

[–]emceelokey 5 points6 points ago

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Actually, the question was valid. It's the teacher that's dumb. That's what's pissing me off. Where was the answer guide and if this kid, the kid that actually got the question right, got it "wrong", did the kids that answered "15 minutes" get it right? Essentially everyone got the question wrong. For anyone that answered "15 minutes" and got it "right", they actually didn't get it right but were told they did and in the end learned nothing. For the kids that answered it legitimately correct, their efforts to actually understand the question not only went unrewarded but were essentially punished by losing points.

[–]motdidr -4 points-3 points ago

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The problem is that it's sort of ambiguous whether you are making 2 equal cuts, or 1 cut and then cutting one of those halves into half, meaning 1 cut half as long. In the first case it's 20 minutes and in the second it's 15.

[–]TheBB 6 points7 points ago

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That is not the problem. Brutally accurate problem statements have no place in grade whatever-this-is, and would serve to confuse more than to clarify. The question is perfectly clear.

"Marie cuts at a constant rate through a right cuboid formed out of a homogeneous medium in two cuts parallell to one of the faces."

Right.

[–]8bitgrafix 0 points1 point ago*

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theres also the direction of cutting to take into account. if she cuts along the x or y axis, front to back, she's cutting more wood. thats where the 20 min vs 15 min possibilities happen because theres different amounts of wood to cut. if she cuts along the z axis, perpendicular to the xy plain right, it should always be 20 min. its a board so it most likely has equal thickness everywhere. it takes the same amount of time to cut through the same amount of wood.

[–]jeanifurr 2 points3 points ago

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I was told there would be no math...

[–]Avsunra 4 points5 points ago

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You should tell your teacher that she should start reading the problems instead of just looking at the numbers

[–]tomkzinti 12 points13 points ago

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Repost.

[–]zburdsal 12 points13 points ago

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EVERYTHING this guy post is a repost. Fucking everything.

[–]caketimenow 1 point2 points ago

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Thats one big piece of wood if it takes 20 mins to cut it into three.

[–]g33n 1 point2 points ago

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My unit in the army ended up at this little shithole building outside Ramadi that we filled with bunkbeds provided by the lowest bidder. Problem was, the bunkbeds weren't rigid enough to bear the weight of someone sleeping on them, so we had to reinforce them with sheets of plywood cut to fit inside the bedframes. However, we only had 4' x 8' sheets of plywood and handsaws; I think it took about two weeks to get acquire all the wood and cut it.

Cutting 8' straight with a handsaw sucks ass, and takes forever.

[–]Bob_Chiquita 4 points5 points ago

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It's a girl using a tool designed for a man, by a man.

[–][deleted] -2 points-1 points ago

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An you're a child using a tool designed for an adult, by an adult.

[–]SirZerty 0 points1 point ago

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to be fair it says "board" not wood. It could be milled steel.

[–]bolt_krank 1 point2 points ago

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Sad state of affairs.

[–]kellyfish22 1 point2 points ago

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Omg is this sunshine math?

[–][deleted] 2 points3 points ago

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Math makes Maeby feel partly cloudy.

http://i.imgur.com/VVxhp.jpg

[–]kilgore_trout89 1 point2 points ago

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Yeah, this isn't even bad compared to a few teachers I've had. We were working on functions and the teacher gave us some problem about how many toys should be produced to reach the maximum profit given a function describing the relation between profit/toys produced (Or some such thing.) She obviously fucked up the problem because when you worked it out you got something like -3283. I wrote 0, because a negative number for units produced would obviously be nonsensical, and because the graph of the function was downward sloping as you approached positive numbers (0 units produced was basically the least amount of profit you were going to lose.)

I end up getting it wrong so I bring it to the attention of the teacher. Apparently if you answered -3283 you got it right, but if you answered 0 you had to write out a sentence or two explaining your answer. God, that lady was such a bitch.

[–]ynks366 0 points1 point ago

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I usually write down the exact number and then explain what it should be if commen sense was used.

[–]RedditRage 1 point2 points ago

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Relevant : http://en.wikipedia.org/wiki/Off-by-one_error#Fencepost_error

[–][deleted] 1 point2 points ago

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Despite the ambiguities, the problem has an illustration next to it which helps to show the type of board and cut that will be used. Using that illustration, the teacher would be incorrect.

[–]Ibonobo 1 point2 points ago

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If the teacher had specified the board was square, the correct answer would have been 15 minutes. (assuming cuts are made at right angles).

[–]truthfulefu 1 point2 points ago

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Teachers are underpaid.

[–]ReadyThor 1 point2 points ago

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Good teachers are underpaid.

FTFY

[–]zagman76 1 point2 points ago

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Logic:

2 Pices = 10 Min

2 Pieces = 1 Cut

1 Cut = 10 Min

3 Pieces = x Min

3 Pieces = 2 Cuts

2 Cuts = 20 Min

[–]napster2k6 -1 points0 points ago

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Who needs 10 minutes to cut a board in half?

[–]Dersuk 4 points5 points ago

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Marie

[–]napster2k6 0 points1 point ago

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Touche.

[–]Intrets 1 point2 points ago

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This picture emerges once in a while so I made this: http://i.imgur.com/RAp0L.jpg

[–]DougLance 1 point2 points ago

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Not if she cuts it lengthwise the first time.

[–][deleted] 0 points1 point ago

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Relevant: http://www.youtube.com/watch?v=_8rg4S3pTsg&feature=player_detailpage#t=44s

[–]LipstickG33k 1 point2 points ago

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I must really suck at math, because even after reading the comments I still don't understand how the teacher messed up. I know that something is wrong, but could someone explain it to me? xD

[–]blahblahmattblah 5 points6 points ago

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it took her 10 minutes to saw it in to two pieces, correct? so she gets another board, takes 10 minutes to saw it into two pieces. Then she takes one part of the two pieces and she takes 10 minutes cut IT into two pieces. Then she's left with 3 pieces.

[–]Slime0 4 points5 points ago

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It only takes one cut to cut a board into two pieces.

It only takes two cuts to cut a board into three pieces.

So the latter should take twice as long as the former.

[–]Mustkunstn1k 1 point2 points ago

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STOP REPOSTING OLD SHIT

[–]Giygas -1 points0 points ago

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YEAH! THIS IS R/PICS. YOU BETTER TAKE THIS SHIT SERIOUSLY GODDAMMIT!!

[–]uzimonkey 0 points1 point ago

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Haha, sunshine math?! I help my niece with this stuff, and I remember this question. If I recall... I want to say her teacher got it wrong too.

[–]nbf1234 0 points1 point ago

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Ten minutes to cut a piece of wood? Is she using a fucking butter knife?

[–]Tiffehx3 0 points1 point ago

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Or maybe she's me and my spindly muscles and unco-ordinated hands.

[–]DarnLemons 0 points1 point ago

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Why are you doing math ment for 7th graders. :l

[–]voetsjoeba 0 points1 point ago

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Delicious irony

[–]DedStarfish 0 points1 point ago

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10 minutes?! Was she using a rusty spoon?

[–]intox310 0 points1 point ago

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I think this problem portrays the differences between physics and Mathematics, mathematically speaking the above is correct, physically speaking the board above shows the truth i.g. 1 cut for two pieces = 10 minutes, 2 cuts = 20.

[–]Amendmen7 0 points1 point ago

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This question blows. The time to cut the board could be almost infinitely small because it doesn't specify that the sections have equal dimension.

Just lop off two corners and bam, problem solved. 0.5 seconds.

[–]mi11er 0 points1 point ago

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If it takes me 10 min to think of a good response. How much is my time worth in karma? Please show your work.

[–]The1stAnon 0 points1 point ago

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this is probably the 4th time ive seen this..

[–]busyp 0 points1 point ago

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question specificity fail more than anything

[–]carebeartears 0 points1 point ago

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20 is right i would think. Cutting the board is a digital operation ie. the board is either cut or it is not cut. At 9.75 min for example u still have the one board and thus one piece. At 10 u have cut the board and now have 2 pieces. So at 20 u would have the 3 pieces.

[–]hillbillyesq 0 points1 point ago

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TIL not to trust reddit doctors-to-be for basic arithmetic.

[–]chbrules 0 points1 point ago

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sin(x)

[–]Moozla 0 points1 point ago

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There are multiple solutions to this question as it is far too ambiguous. Lets say we have a 10mx10m board. She works at a rate of 1m cut per minute, she makes the cut directly down the middle.

Now we are left with two pieces each being 10mx5m. She can now cut along the smaller edge of the board which is 5m long. This would take 5mins working at the same rate.

Thus the answer IN THIS CASE is 15 minutes. The question is far too ambiguous to say any particular answer is wrong.

edit: However going by the diagram that is shown, the answer of 20minutes makes sense

[–]genk 0 points1 point ago

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Math is the worst

[–]shakeyjake 0 points1 point ago

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If fails to take into account that with each cut the saw is dulled so the cutting ability would deteriorate. So it would take 10 minutes + the time to account for the duller saw.

[–]Razziaro 0 points1 point ago

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you fail XD

[–]jmls10thfloor 0 points1 point ago

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actually the kid was wrong too. if 10 mins = 2 pieces = 1 cut twice as fast = 5 mins per cut 3 pieces = 2 cuts = 10 mins at the twice as fast speed.

[–]SomeAudioGuy 0 points1 point ago

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6÷2(1+2)=?

[–]drgradus 0 points1 point ago

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Do the pieces have to be cut parallel? Because, in the case of a square board, if you used the first 10 minutes to cut the board into half, you would only need 5 minutes to halve one of the halves. (I guess the approach you're taking is that of the halve-not).

[–]Blaculahunter 0 points1 point ago

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Where are people getting these square boards that take ten minutes to cut. I never go to a lumber yard and spot a big square board, unless it is plywood, which isn't a board and a handsaw wouldn't be used and any power saw wouldn't take ten minutes unless the board was mega gigantic. Any accuracy would need a skil or table saw. This is a stupid question to begin with.

[–]dmalice -2 points-1 points ago

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Really? Do we need to have this pointless discussion AGAIN?

This is called AMBIGUITY

[–]Slime0 2 points3 points ago

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To be fair, right next to the problem is a picture of a very long and thin board being cut by a saw.

[–]TheBB 1 point2 points ago

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"Marie cuts at a constant rate through a right cuboid formed out of a homogeneous medium in two cuts parallell to one of the faces."

Would you have preferred something like that for a grade whatever-this-is student?

The problem as stated is perfectly clear. Ambiguity has nothing to do with it.

[–][deleted] 0 points1 point ago

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I wouldn't call that ambiguity. Instead you're elaborating on the meaning of the question enough to get a wrong answer to work.

[–]Blaculahunter -3 points-2 points ago*

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Well, in all honesty, if you had "board" like that, a skil saw or table saw would be used. Usually a regular board wouldn't be square like that. Maybe a sheet of ply wood that had already been cut would, unless you are using a handsaw on the top of a 4x4. If it takes you five minutes for one cut and ten for another, you are in the wrong profession.

[–]opiemonster -1 points0 points ago

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The answer is 0.0707106781186548

read below I show you why...

Equations

work = energy/time

workload = cuts/time

Variables:

cutsA=1 (saw board into 2 pieces = 1 cut)

cutsB=2 (saw board into 3 pieces = 2 cuts)

timeA=10 (10 mins to saw a board)

timeB=?

workloadA = CutsA/timeA

workloadB = CutsB/TimeB

Calculation: she works "just as fast" for workload a as she does for b

workloadA = cutsA/timeA2 = cutsB/timeB2

so

1/100 = 2/timeB2

squareroot(1/200) = timeB

= ~ 0.0707106781186548

if you think its timeA=timeB instead of cutsA/timeA2 = cutsB/timeB/2

then you would be saying 1=2 i.e.

1/10 = 2/10

1=2

:D (Note the question said that she works at the same speed, meaning the speed of work which is energy/time/time which = energy/time2

[–][deleted] ago

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[deleted]

[–]Blaculahunter 14 points15 points ago

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Yes, that is the point of this picture. Good job! Now, on to grammar class.

[–][deleted] -1 points0 points ago

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It makes sense to me, you have a board, you cut off one piece from the end, in 5 minutes, then cut off another piece in 5 minutes .. you've cut off 2 pieces from that board. (2 cuts gives you 2 pieces, the original stock does not count as a piece).

[–]dmalice -1 points0 points ago

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the wording "saw a board into [number of] pieces" makes it pretty clear that the question cannot be interpreted the way you have stated.

*edit - although it's possible this was the source of the teacher's mistake.

[–][deleted] 0 points1 point ago

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ahh gotcha, as opposed to 'cut [number of pieces] from'.. yeah I guess it was just worded very poorly.

[–][deleted] ago

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[deleted]

[–]dmalice 3 points4 points ago

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1 piece = 0 minutes. The board is already 1 piece.

[–][deleted] ago

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[deleted]

[–]Thecardinal74 10 points11 points ago

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2 pieces = 1 cut, which took 10 minutes. 3 pieces = 2 cuts, each at 10 minutes.

[–]samwisevimes 8 points9 points ago

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cough I knew that, was just testing cough

[–]Akbd40 2 points3 points ago

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Should be samnowisevimes

[–]khutchins10 0 points1 point ago

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He was testing you, and you passed.

[–]lif1441 4 points5 points ago

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It takes 10 minutes to cut a piece of wood into two pieces (one cut).

Therefore it would take 20 minutes to cut a piece of wood into three pieces (two cuts).

Math teacher fail.

[–]Trashcanman33 -1 points0 points ago

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Yea it's just poorly worded, I'd be impressed if the student arrived at 20 cause he actually thought 10 mins per cut. Most likely he just got it wrong and a parent noticed how stupid the question is.

[–]Aitioma -1 points0 points ago

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  1. Send my kid to a private school where teachers get fired after such a fuckup.

Wait... that's all.

[–]lestratege -1 points0 points ago

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Well, if she sawed a board that was 1m by 1m into two pieces of 1m by 0.5m and then proceed to saw one of the cut piece (1m by 0.5m) into two pieces of 0.5m by 0.5m, working as fast, then indeed, it will take Mary 15 min.

The timing of cut has nothing to do with how many pieces are cut, but depends on the length cut.

If Mary saw the first board in diagonal, and then cuts off just the tip of one of the pieces, she could saw the board in three pieces in 10m 30s working just as fast.

The failure is not about the answer, the failure is about whoever came up with that stupid problem.

[–]noekinney4349 -1 points0 points ago

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combine this teacher with the no child left behind act...and this countrys going somewhere.

[–]JipJopJones -2 points-1 points ago

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Had this same question on a test when I was in highschool, I answered 15 and I was marked wrong. I never let that go.

[–]ryegye24 1 point2 points ago

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15 is wrong. The answer is 20.

[–]JipJopJones 1 point2 points ago

sorry, this has been archived and can no longer be voted on

sorry, typo on my part... I meant to say I said 20 and was mark wrong, the teacher claimed the answer was 15.

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