I looked at a textbook used by a hagwon in Busan and found this question. It was one of ten using marine invertebrate zoology to teach math.My problem is, the math seems quite challenging; well, for elementary school students (good save, Surprises!).

This answer (12) is way off, isn’t it?

Seeing this very simple calculation made me lose confidence somewhat. I had to draw a picture before being willing to throw the given answer away and work it out.

In case anyone is interested in working it out, the answer is some distance below. Scroll down when ready.

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I compared the result of halving the numbers for the radius, squaring and multiplying by π.

That result being (45 squared *π)/(3.75 squared*π)= 6,361/44.175 = 144

If you’re curious, yes, I did leave in π in both locations instead of canceling them out.

Calculators do make you lazy, but I think I still know how to do some math.

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This entry was posted on July 8, 2011 at 9:49 pm and is filed under education. You can follow any responses to this entry through the RSS 2.0 feed.
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July 9, 2011 at 1:24 am |

I got 144 before scrolling down to see your results, and I followed exactly the method you did. You’re not crazy. But now, thanks to your having found that mistake, you might

becomeparanoid: what ifmanyanswers in that book are wrong?I deal with that problem rather frequently at my current job. The answer keys for many of our company-made texts are rife with errors– some of which are caught by the teachers, some of which are caught by the students. It’s frustrating, though it can also be fun, since it gives both the teachers and the students a chance to mock the textbook-makers.