Question

Suppose that a small pump can empty a swimming pool in 70 hours and that a large pump can empty a pool in 30. Working together, how long will it take to empty the pool?

Answer 1

s = small pump flowrate = 1 / 70

L = large pump flowrate = 1/30

(1/70  + 1/30) *t = 1

10/210 t = 1

t = 21

Hope this helps