Find two positive real numbers whose product is a maximum. (Enter your answers as a comma-separated list.)
The sum of the first and twice the second is 20.
first number --- y
2nd number ---- x
given: y + 2x = 20
y = 20-x
product = xy
= x(20-2x)
= 20x - 2x^2
compare this with f(x) = -x^2 + 20
which is a parabola opening downwards, so all you have
to do is find the vertex and you got it.
Normally we would use Calculus and finish it in 2 steps, but
since you are naming your subject Pre-Calculus .....