### Home > PC3 > Chapter 3 > Lesson 3.1.5 > Problem3-69

3-69.

The sum of two numbers is $60$. Determine the numbers so that their product is the greatest.

Let $x=1$st number
Let $y=2$nd number
Let $P=$ the product
$x+y=60$
$P=xy$

1. Solve the first equation for $y$ and substitute the result in the second equation.
2. Check where the graph of $P$ is a maximum.