In what universe is the more accurate answer wrong? Reading carefully so that you see the word "about" doesn't make the answer *wrong*. If they want the kids to practice estimation, they should say "use estimation." But even then it's unclear what would be the "right" answer. Estimating can be to varying degrees of precision. 45,600 would be a reasonable estimate.

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."