The flow rate for one pipe is 2 times that of another pipe. A swimming pool can be filled in 10 hours using both pipes. Find the time required to fill the pool using only the pipe with the lower flow rate.

Pipe 1 twice as fast as pipe 2.

(Pipe 1 time * Pipe 2 time) / (Pipe 1 time + Pipe 2 time) = combined time

(x * (x/2)) / (x + x/2) = 10

(x^2/2) / 1.5 x = 10

x^2 / 2 = 15 x

x^2 / 2 - 15 x = 0

x = 30 (slow pipe)

x/2 = 15 (fast pipe)

So it would take 30 hours using the slow pipe only.