Two water pumps are filling a pool. One of the pumps is high power and can fill the pool 5 hours before the other can do. However, they both working together can fill half of the pool in 3 hours. In how many hours the high power pump can fill the pool?
If the fast pump can fill it in x hours, then the slow pump takes x+5 hours. So, now you know that
1/x + 1/(x+5) = (1/2)/3
So just find x