Question

nguyen can earn $5 and hour for working at the college library and $9 an hour for construction work. To save time for study, he wants to limit his work to 20 hours a week but still earn more than $125. how many hours can he work in the library?

Answer 1

The answer is 13 days.

Explanation:

Let's call the days he can work in the library x.

The days he can work in construction work is 20-x. Then x days per 5$ plus (20-x) days per 9$ should be bigger than 125$.

`5x+9(20-x)>125`

`5x+180-9x>125`

`55>4x` therefore
`13,75>x`

Since x must be integer, the biggest we choose is 13.

To crosscheck

`13.5=65` →
`(20-13).9=63` →
`65+63=128`