# Can you solve this 7th grade math problem? **URL:** \ **Category:** In My Humble Opinion\ **Created:** [December 3, 2003, 3:27am UTC](https://boards.straightdope.com/t/can-you-solve-this-7th-grade-math-problem/216634 "2003-12-03T03:27:47Z")\ **Posts on this page:** 13\ **Page:** 3
**Author:** ![Shodan](https://avatars.discourse-cdn.com/v4/letter/s/9f8e36/32.png) [@Shodan](https://boards.straightdope.com/u/Shodan)\ **Post date:** [December 4, 2003, 3:37pm UTC](https://boards.straightdope.com/t/can-you-solve-this-7th-grade-math-problem/216634/41 "2003-12-04T15:37:02Z")
I estimated it at 2/5, on the logic that 3/8 is almost one half. 1/2 = 5/10 5/10 - 1/10 = 4/10 reduced to 2/5. My “rule” of estimating is to set up the problem so the math is easy to solve, rather than the strict rules, but if the strict rules come up with an answer that is obviously wrong, to heck with the strict rules. The purpose of estimating is as a practical shortcut, and a shortcut that comes up with an answer that is wrong is worthless. I thought modern math education was about learning to think clearly, rather than mindlessly applying rules. Regards, Shodan ---
**Author:** ![Dag\_Otto](https://avatars.discourse-cdn.com/v4/letter/d/439d5e/32.png) [@Dag\_Otto](https://boards.straightdope.com/u/Dag_Otto)\ **Post date:** [December 4, 2003, 6:31pm UTC](https://boards.straightdope.com/t/can-you-solve-this-7th-grade-math-problem/216634/42 "2003-12-04T18:31:39Z")
Of course, there is no right answer. Some estimates are just better than others. Given that, I wonder if the question wasn’t posed as a multiple choice question. \*Using estimation , what is 3/8 - 1/10? a) 0 b) 1/2 c) 1 d) 2\* If posed in that manner, then 1/2 is the ‘correct’ answer. However, the real learning would be in the class discussion that follows. If the teacher were any good, he would be sure to have the kids talk about how and why they arrived at their answers. Otherwise, kids who didn’t ‘get it’ wouldn’t be any better off. ---
**Author:** ![SlowMindThinking](https://avatars.discourse-cdn.com/v4/letter/s/dc4da7/32.png) [@SlowMindThinking](https://boards.straightdope.com/u/SlowMindThinking)\ **Post date:** [December 4, 2003, 7:35pm UTC](https://boards.straightdope.com/t/can-you-solve-this-7th-grade-math-problem/216634/43 "2003-12-04T19:35:10Z")
I have several kids in this age bracket, and teaching estimation is “in”. IMHO, teaching estimation is probably more important than teaching any one calculational skill. But then, my Ph. D. is in physics, and many physicists take pride in knowing how to estimate, so maybe I’m biased. I have noticed that the reason physicist take so much pride in estimating is that so many people are bad at it. (I used twickster’s method, except that I immediately went from 22/80 to 1/4th, btw.) Estimation does need to be taught, because it is unnatural to so many people. (And it prevents that Paris Hilton problem of trying to buy $65 worth of groceries with $50.) Yes, the book’s approximation is bad. But perhaps the next step is to show how to make better estimates with small numbers, fractions, and division. My kids were taught to use their head, but they were also taught several techniques, so that they had several alternatives to choose from. No technique is good in all situations, and kids need to see that. ---
**Author:** ![Rhum\_Runner](https://avatars.discourse-cdn.com/v4/letter/r/2bfe46/32.png) [@Rhum\_Runner](https://boards.straightdope.com/u/Rhum_Runner)\ **Post date:** [December 4, 2003, 8:29pm UTC](https://boards.straightdope.com/t/can-you-solve-this-7th-grade-math-problem/216634/44 "2003-12-04T20:29:49Z")
You should go talk to the teacher, obviously he/she didn’t write the book, but you should make sure they recognize that this is wrong etc… And ditto to what everyone else said. Incidnelty I simply converted 3/8 to 80ths, subtracted 1/10, divided out the 2 and had the exact answer in less than two seconds, I would expect anyone beyond the third grade to be able to do so as well. ---
**Author:** ![rkts](https://avatars.discourse-cdn.com/v4/letter/r/c4cdca/32.png) [@rkts](https://boards.straightdope.com/u/rkts)\ **Post date:** [December 5, 2003, 2:48am UTC](https://boards.straightdope.com/t/can-you-solve-this-7th-grade-math-problem/216634/45 "2003-12-05T02:48:41Z")
> [@](#): > > Approximations and estimations are an important skill, and I’m rather happy to hear that it’s been taught in school. I’m not. Once one can do math accurately, estimation either comes naturally or becomes, as in this case, entirely unnecessary. It should be through experience that one learns to use 3 as pi when estimating the size of a tennis ball, but not when calculating the size of the earth; if you have to learn that from a textbook, it’s just one more inconvenient thing to have to memorize, and you aren’t likely to remember it. ---
**Author:** ![rkts](https://avatars.discourse-cdn.com/v4/letter/r/c4cdca/32.png) [@rkts](https://boards.straightdope.com/u/rkts)\ **Post date:** [December 5, 2003, 3:05am UTC](https://boards.straightdope.com/t/can-you-solve-this-7th-grade-math-problem/216634/46 "2003-12-05T03:05:29Z")
I meant to rephrase that before hitting Submit. I really did. Here’s a better shot at it: It should be by numerical experience that one knows to use 3 as pi when estimating the size of a tennis ball, but not when calculating the size of the earth. Meaning, you don’t have to have estimated the size of a tennis ball or of the earth before, but you do have to have experience with the relative consequences of multiplying 0.14159… by such large numbers as the size of the earth, and of multiplying it by such small numbers as the size of a tennis ball. It is a matter of proportions, the feeling for which can only be acquired through practice. ---
**Author:** ![gyt\_fx](https://avatars.discourse-cdn.com/v4/letter/g/74df32/32.png) [@gyt\_fx](https://boards.straightdope.com/u/gyt_fx)\ **Post date:** [December 5, 2003, 3:29am UTC](https://boards.straightdope.com/t/can-you-solve-this-7th-grade-math-problem/216634/47 "2003-12-05T03:29:54Z")
Im in High school, and I remember I **learned** math back when it was taught 3rd-8th grade. The latest books being used are “integrated,” so they aren’t really geometry, trig, pre-cal, etc… It’s integrated 2, 3, 4 etc… You answer math questions in words most of the time, about 1/4th of it is actual math that is usefull. It’s pretty terrible, math was my favorite subject and now since they have that gay math program I got my required math credits and I’m done. ---
**Author:** ![Briny\_Deep](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/briny_deep/32/17188_2.png) [@Briny\_Deep](https://boards.straightdope.com/u/Briny_Deep)\ **Post date:** [December 5, 2003, 3:57am UTC](https://boards.straightdope.com/t/can-you-solve-this-7th-grade-math-problem/216634/48 "2003-12-05T03:57:58Z")
Ooh, a gay math program! _The answer is 25, because 25 is more **fabulous** than 24!_ ---
**Author:** ![ouryL](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ouryl/32/6067_2.png) [@ouryL](https://boards.straightdope.com/u/ouryL)\ **Post date:** [December 5, 2003, 4:47am UTC](https://boards.straightdope.com/t/can-you-solve-this-7th-grade-math-problem/216634/49 "2003-12-05T04:47:38Z")
This problem reminds me of how I once incredulously watched a freind of mine try to average percentages. ---
**Author:** ![RickJay](https://avatars.discourse-cdn.com/v4/letter/r/bb73d2/32.png) [@RickJay](https://boards.straightdope.com/u/RickJay)\ **Post date:** [December 5, 2003, 4:57am UTC](https://boards.straightdope.com/t/can-you-solve-this-7th-grade-math-problem/216634/50 "2003-12-05T04:57:12Z")
I converted the fractions to decimals in my head, THEN figured it out. Like all true baseball fans, I know that 3 for 8 is .375, and 1 for 10 is .100, and just went from there. ---
**Author:** ![cmkeller](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cmkeller/32/118_2.png) [@cmkeller](https://boards.straightdope.com/u/cmkeller)\ **Post date:** [December 5, 2003, 5:09am UTC](https://boards.straightdope.com/t/can-you-solve-this-7th-grade-math-problem/216634/51 "2003-12-05T05:09:45Z")
Was this a 1920’s-style math textbook? ---
**Author:** ![Naive\_Theory](https://avatars.discourse-cdn.com/v4/letter/n/b5ac83/32.png) [@Naive\_Theory](https://boards.straightdope.com/u/Naive_Theory)\ **Post date:** [December 5, 2003, 5:27am UTC](https://boards.straightdope.com/t/can-you-solve-this-7th-grade-math-problem/216634/52 "2003-12-05T05:27:18Z")
FWIW, I’ve never met a qualified mathematician who approves of the k-12 math program. One of my professors is especially bothered by the program, and often laments how mathematicians are all but barred from the developement of the curriculum and textbooks where I live. Instead, education majors with a ‘focus’ in math are responsible. By my estimate, the ‘focus in mathematics’ requirements of the education degree can be completed in two semesters. ---
**Author:** ![Dr\_Paprika](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr_paprika/32/3042_2.png) [@Dr\_Paprika](https://boards.straightdope.com/u/Dr_Paprika)\ **Post date:** [December 5, 2003, 6:31am UTC](https://boards.straightdope.com/t/can-you-solve-this-7th-grade-math-problem/216634/53 "2003-12-05T06:31:37Z")
Obviously it is easy to figure out the exact answer. I would have said 3/8 is approximitely (4/10) and subtracted 0.1 to get 0.3 (3/10) Clearly the problem has many answers, some of which suck. [Previous page](https://boards.straightdope.com/t/can-you-solve-this-7th-grade-math-problem/216634.md?page=2)