The detailed answer was wrong because of significant figures: when multiplying, your answer can only have as many significant figures as the least accurate number you start with. So when the problem said "about 8" it was throwing out ONE significant figure. Ergo, the answer cannot include more than ONE significant figure.

This means that the math book was also wrong. The correct answer is 50,000. 5,678*8=45,424. You round up to 50,000, which has only one significant figure (the 5).

And I have no idea where "48,000" came from (please tell me it was a typo). Did they just pull that out of the air? ETA: Oh, I get it now. They rounded FIRST, and then multiplied, and failed to account for sig. figs. This is painful. The rule is: multiply first with whatever you have, then round. Ouch. This really hurts.

I wouldn't expect someone learning multiplication to understand significant figures. But the people who wrote the book should, and they should have specified the necessary information, such as "round to the nearest x." You still have to read the problem to get that information and yet putting it there also removes the need to guess.


Originally Posted by MegMeg
Sheesh, I swear this stuff comes from some Bizarro Totalitarian Alternate Reality, where "words mean what I say they do, because I'm in charge."

Agreed.

Last edited by Val; 11/26/12 04:33 PM.