Asked by Rob

It takes an older pump 4 times as long to drain a certain pool as it does a newer pump. Working together, it takes the two pumps 4 hours to drain the pool. How long will it take the older pump to drain the pool working alone?
Answered by Steve
If the fast pump takes x hours, then

1/x + 1/(4x) = 1/4

Solve for x, and then use 4x as your time.