Answer:
6 hours
Step-by-step explanation:
We can think of this problem as a "work" problem and use the formula:
work = rate x time
Let p be the rate of a single pump. So the total rate of 3 pumps is 3p. And the total time is 8 hours, so the work needed to fill a pool is:
work = 3p x 8 = 24p
We need 24p to fill up a pool.
So what happens when you have 4 pumps? That is a rate of 4p. So how much time is needed to fill up a pool that requires 24p of work?
Solve by using the work = rate x time equation:
24p = 4p x t
6 = t
6 hours.
