Question

Three water pipes are used to fill up a swimming pool. The first pipe alone takes 8 hours to fill the pool, the second pipe alone takes 12 hours to fill the pool, and the third pipe alone takes 24 hours to fill the pool. If all three pipes are opened at the same time, how long will it take to fill the pool?

Answer 1

In an hour, the first pipe can fill up 1/8 of the pool
In an hour, the second pipe can fill up 1/12 of the pool
In an hour, the third pipe can fill up 1/24 of the pool.

So, in an hour, the 3 pipes can fill up 1/8 +1/12 + 1/24 = 6/48 + 4/48 + 2/48 = 11/48 of the pool.

It will take the 3 pipes 1 : 11/48 = 48/11 hours to fill the pool.