Question

It takes 20 minutes to fill a wading pool. The pool has developed a leak through which it will empty in 30 minutes.

Answer 1

In t minutes, t/20 of the pool is filled and t/30 of it is emptied.

t/20 - t/30 = 1
multiply both sides by LCM 60.

3t - 2t = 60
t = 60

The pool is filled in 60 minutes.