The pool can be refilled in 3 hours and poured out of an open pipe in 5 hours.

The pool can be refilled in 3 hours and poured out of an open pipe in 5 hours. How long does it take if the pool is poured with an open pipe?

Let’s designate a fully filled pool as a unit. Then the pool fill rate is 1/3 bass / h and the outflow rate is 1/5 bass / h. Let’s find the speed of filling the pool with an open pipe, for this we subtract the speed of filling with a closed pipe, the speed of pouring water from the pool:

1/3 – 1/5 = 5/15 – 3/15 = 2/15 bass / h.

To find when the pool will fill when the pipe is open, divide 1 by the resulting velocity:

1 / 2/15 = 15/2 = 7.5 hours.

Answer: with an open pipe, the pool will need to be poured until it is full for 7.5 hours.