text: derivative help: word problem? question: find two (2) positive (+) numbers such that one and four times equals 1000, and the product of the two is a maximum.   where to start with this problem? thanks. 4x+y=1000 p=xy =x(1000-4x) =1000x-4x^2 dp/dx=1000-8x setting this to zer 8x=1000 x=125 the numbers are 500and 125