Question 302994
One inlet pipe can fill an empty pool in 4 hours, and a drain can empty the pool in 10 hours. How long will it take the pipe to fill the pool if the drain is left open?


fills in 4 hours 

it can do 1/4 of filling job in 1 hour

Drains in 10 hours

It can do 1/10 of draining job in 1 hour

the difference is the effective filling job done in 1 hour

1/4-1/10

5-2 /20

3/20 job in 1 hour

20 /3 hours it takes to fill when drain is open

6.66 hours

Ananth