It takes three identical water pumps 8 hours to fill a pool. How long would it take four of the same pumps to fill the pool?

Answer 1

Let x = the number of hours each pump would take to fill the pool, working alone.

(3/x) = 1/8 => x = 24

At that rate 4 pumps will fill the pool in y hours where

(4/24) = 1/y

y=6

Note: Each pump fills 1/24 of the pool per hour