A “simple” 3rd grade problem • Hacker News Board

Re: A “simple” 3rd grade problem

#61

Post by 0003 » Sat, May 04, 2013, 5:08 PM UTC

quacker wrote: post #41

jrabone wrote: post #27

Earlier quoted context omitted.

It is ABSOLUTELY open for debate, and part of the clue is in the question "if she works just as fast" ie. the cutting rate is constant. Then, it is ambiguous since the SIZE of the pieces is not mentioned. It's not the teacher's fault, per se; the question is unanswerable. The student picked one interpretation but the (likely) correct one is shown in the answer http://math.stackexchange.com/a/380007

In reality, it probably was not open for debate. This is third grade math, remember. The student probably spent the last three problems working similar questions covering ratios/fractions. And the student probably spent at least a few weeks of school working similar types of problems on homework. After so long taking these types of classes and tests, if a student answers a question without using knowledge gained from…

I would assume that the "*" next to the problem was an indication that this what not a 'time to fill a water bucket' problem and that more thinking would be required than the previous 3 problems.

Re: A “simple” 3rd grade problem

#62

Post by chacham15 » Sat, May 04, 2013, 5:09 PM UTC

downandout wrote: post #15

The student is absolutely correct. I don't think it's even open for debate. Cutting anything in half requires exactly one cut; cutting in thirds requires two. It's as simple as that. The teacher that crafted the question, or worse yet, the publisher of a textbook that may have provided the test question, needs to take a hard look at whether or not they are in the correct profession. The fact that the teacher not only…

While, given the picture presented the child's solution makes the most sense, there is another close scenario in which the teacher is correct[1]. So its not really "as simple as that."

[1]http://math.stackexchange.com/a/380007

Re: A “simple” 3rd grade problem

#63

Post by doorhammer » Sat, May 04, 2013, 5:11 PM UTC

shurcooL wrote: post #25

downandout wrote: post #15

The student is absolutely correct. I don't think it's even open for debate. Cutting anything in half requires exactly one cut; cutting in thirds requires two. It's as simple as that. The teacher that crafted the question, or worse yet, the publisher of a textbook that may have provided the test question, needs to take a hard look at whether or not they are in the correct profession. The fact that the teacher not only…

You can't tell if it was a simple "whoops, I thought this question belonged to a problem category X, and I overlooked that it does not" typo-like mistake, meaning the teacher would instantly realize his/her mistake if you point it. Or if they wouldn't get it even after you try to explain it to them (what you're trying to imply here). When grading things, ppl usually face hundreds of copies at a time and it's very ted…

I agree with this. I think it's a pretty decent example of the fundamental attribution error.

The context of the problem clearly sets it up as one of those "everyone gets this wrong, so make sure you think a second" situations (I had to think a second, anyway).

I'd extend that to the publisher as well, though (or at least it's individual employees creating the book). First off, assuming the answer key has "15", I'm not in any way saying it's okay that we have text books teaching clearly incorrect information; I'm also not in the know on how 3rd grade math textbooks are created. That said, I've been in tons of jobs where you're expected to produce a crap ton of work at a breakneck pace and god help you if you want five minutes to check your work for dumb errors, because y'aint gettin it.

Of course, it could also easily be said that this is also the publishers fault for creating a working environment that isn't sufficiently rigorous or overburdens the employees.

Re: A “simple” 3rd grade problem

#64

Post by gfunk911 » Sat, May 04, 2013, 5:13 PM UTC

viraptor wrote: post #13

Oh the "simple" questions... reminds me of the fragment from Cryptonomicon where Lawrence Waterhouse answering the usual trivial math question about boat going from A to B with some speed X while the water moves with speed Y. He failed, even though he decided the answer cannot be that trivial and wrote a long solution involving analysing the flow of the water using partial differential equations (later published in a…

As which point they decide he is qualified to play a glockenspiel.

Re: A “simple” 3rd grade problem

#65

Post by henrik_w » Sat, May 04, 2013, 5:15 PM UTC

Just asked my 10-year-old the question. He thought for 5 seconds and answered 20 minutes.

Re: A “simple” 3rd grade problem

#66

Post by monkeynotes » Sat, May 04, 2013, 5:18 PM UTC

chacham15 wrote: post #62

downandout wrote: post #15

The student is absolutely correct. I don't think it's even open for debate. Cutting anything in half requires exactly one cut; cutting in thirds requires two. It's as simple as that. The teacher that crafted the question, or worse yet, the publisher of a textbook that may have provided the test question, needs to take a hard look at whether or not they are in the correct profession. The fact that the teacher not only…

While, given the picture presented the child's solution makes the most sense, there is another close scenario in which the teacher is correct[1]. So its not really "as simple as that." [1] http://math.stackexchange.com/a/380007

Yes, the question did not account for unknown specifics. There is also a 3rd answer which in which the answer accounts for the person making the cuts having to answer the phone half way through the job.

Re: A “simple” 3rd grade problem

#67

Post by danso » Sat, May 04, 2013, 5:22 PM UTC

This question is easy in hindsight. The fact that it's been prefaced as something "simple" makes you scrutinize it much more closely than if you were someone grading a series of questions en masse...because you've been warned that it's not so simple.

That said, this gave me a little glimmer of hope about the state of logic education, at least among our third grade students.

Re: A “simple” 3rd grade problem

#68

Post by keithpeter » Sat, May 04, 2013, 5:24 PM UTC

downandout wrote: post #15

The student is absolutely correct. I don't think it's even open for debate. Cutting anything in half requires exactly one cut; cutting in thirds requires two. It's as simple as that. The teacher that crafted the question, or worse yet, the publisher of a textbook that may have provided the test question, needs to take a hard look at whether or not they are in the correct profession. The fact that the teacher not only…

Yes. This is the '10 posts, nine spaces' problem.

Here is another version:

A fence is made using 15 posts spaced equally along a straight line. There are 3m between each post. What is the distance between the first and last post?

When I'm teaching this kind of thing, we go out and walk around the building site opposite with a few 15m measuring tapes. The physical walking out and measuring helps.

Re: A “simple” 3rd grade problem

#69

Post by keithpeter » Sat, May 04, 2013, 5:26 PM UTC

shurcooL wrote: post #25

downandout wrote: post #15

The student is absolutely correct. I don't think it's even open for debate. Cutting anything in half requires exactly one cut; cutting in thirds requires two. It's as simple as that. The teacher that crafted the question, or worse yet, the publisher of a textbook that may have provided the test question, needs to take a hard look at whether or not they are in the correct profession. The fact that the teacher not only…

You can't tell if it was a simple "whoops, I thought this question belonged to a problem category X, and I overlooked that it does not" typo-like mistake, meaning the teacher would instantly realize his/her mistake if you point it. Or if they wouldn't get it even after you try to explain it to them (what you're trying to imply here). When grading things, ppl usually face hundreds of copies at a time and it's very ted…

"When grading things, ppl usually face hundreds of copies at a time and it's very tedious."

Oh, yes, been there and I have the video. Don't you work from pre-written and checked marking schemes?

Re: A “simple” 3rd grade problem

#70

Post by GuiA » Sat, May 04, 2013, 5:29 PM UTC

s_kilk wrote: post #26

auctiontheory wrote: post #20

A friend of mine teaches school in rural North Carolina - here's what she tells me. Her school has to meet certain percentage-based "standards" - I forget the exact numbers, but let's say 75% is the cutoff. So now when Joey gets 5 answers right out of 10, the resulting 5/10 is defined as "75%." We're doomed.

Wait... How on earth do they justify redefining 50% as 75% ? (or whatever the actual numbers are)

It's called grading on a curve, and it's (imo, unfortunately) very common in undergraduate courses in the US :)