神級數學題 9成人都答錯！

shadeslayer

原帖由 1234ats 於 15-11-19 發表
The question asks for a reasonable answer.

75 is not only a reasonable but also an absolute correc ...

"Reasonable estimate" sounds better.

In estimation, the rounding off "is" not precise. And no need to be precise.

1234ats

shadeslayer
In estimation, the rounding off "is" not precise. And no need to be precise.
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I'm not sure about that. How about approximation? Does the rounding off for approximation has to be precise?

Just for the sake of argument, if rounding off for estimate can be arbitrary chosen then 103-28=75 should also be a correct estimate because it is based on rounding off to the nearest integer.

Cheeselover

原帖由 Cheeselover 於 15-11-19 發表
I can say that again. Reasonable means sound judgement, based on good sense or able to reason logica ...

Don't know  why my message was lost in transmission. Whatever, 8 - 3, the answer could be 5, >0 or

caa

This kind of questions obviously aim to trick the kids. Why can't the question be set as "Is 70 a reasonable answer?" I can't figure out what purpose the teacher wants to achieve thru this question other than to discourage the kids.

shadeslayer

原帖由 1234ats 於 15-11-19 發表
shadeslayer
In estimation, the rounding off "is" not precise. And no need to be precise.
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I think the essence of approximation is rounding an awkward number to a number close enough to the original number but is much easier to handle arithmetics. There is no rule in terms of rounding to how many significant figures, or integer, or even numbers, etc. everybody may have slightly different views.

103 -> 100 easy to understand
106 -> ? For this I would still use 100.  You may be different.

cow

Dear Parent/Guardian,

Many times in real life, an exact answer is not needed and an estimate will do......The rules for “rounding” that you may have learned in school are
purposely not taught at this level [grade 2]......

for example, to estimate 84 – 39, you could think 84 – 40 = 44.

This subtraction is easy to do mentally because the second number (40) has been converted to the closest multiple of ten. Note that converting the first number to a multiple of 10 (80 – 39) does not make the subtraction easier.
http://www.nthurston.k12.wa.us/c ... in/1439/2_LH_M9.pdf

cow

Using Compatible Numbers to Estimate Answers

Mathematicians sometimes estimate answers to addition and subtraction problems
by using compatible numbers. Compatible numbers are numbers that work
well together. If a pair of numbers is easy to add or subtract, those numbers are compatible. For example:

Tonio collects sports cards. He has 17 football cards and 26 baseball cards. About how many cards does he have in all? About how many more baseball than football cards does he have?
17 is close to 15
26 is close to 25
15 + 25 = 40, so he has about 40 cards in all.
25 – 15 = 10, so he has about 10 more baseball than football cards.
http://www.sw.wednet.edu/site/ha ... eName=EstAddSub.pdf

shadeslayer

原帖由 cow 於 15-11-19 發表
Using Compatible Numbers to Estimate Answers

Mathematicians sometimes estimate answers to addition  ...

These references actually support what I said in my earlier posts.

cocokan2004

如果全班90%小朋友都識答, 我5會話出題有問題囉.  如果大部份人都錯就係出錯問題或老師根本無教過ESTIMATION. 無講清楚佢直家唔想玩MATHS, 玩ESTIMATION.

你問我你有109元, 拿走12元. 我用0.1秒找到PRECISE答案.  但你話一定要用ESTIMATION, 我反而要用幾秒去ROUND UP.   條題簡單到ESTIMATE唔到.  玩得ESTIMATE, 應該係出一些題目是"找ESTIMATE 答案快過PRECISE答案".

hkpapa852

cocokan2004 發表於 15-11-19 18:45
如果全班90%小朋友都識答, 我5會話出題有問題囉.  如果大部份人都錯就係出錯問題或老師根本無教過ESTIMATIO ...

如果話問緊"estimation"既答案, 但個"estimation"太準確而當錯, 根本就唔合理

Estimation係估計, 但估計都可以係準確, 所以答75一定唔可能話錯.

要話錯, 只能話個學生唔應該以calculation by exact figures既方式去解釋個答案.

shadeslayer

原帖由 frederickw 於 15-11-21 發表
有趣的是, 我完全唔明點解你覺得 there is a cue that the question is testing approximation.

剩睇條題 ...

As I said this is interpretation of English and English is not precise, especially by people like us, non native speakers. I had that feeling, you may not. I have given my reasons before and I am not going to repeat.