Question

It takes three identical water pumps 8 hours to fill a pool. c How long would it take four of these same pumps to fill the pool, assuming they all pump at the same rate?

Answer 1

6 hours

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.