Question

A new type of pump can drain a certain pool in 4 hours. an older pump can drain the pool in 6 hours. how long will it take both pumps working together to drain the pool? do not do any rounding.

Answer 1

Work in fractions of the pool the pumps can drain per hour:-

1/6 + 1/4  = 1/x     where x is the time to drain the pool by the 2 pumps together

4x + 6x = 24
10x = 24
x = 2.4  hours  <===== answer