Question 472409
Wow, I'm actually an AoPS member (but then there's no book called "What would Euler eat")...


Assuming it sells 720 - 10n books at a price of n dollars, we can say that the revenue is n(720 - 10n) = -10n^2 + 720n. This is a parabola, in which the vertex occurs at the vertex n = 720/(2*10) = $36.