Question

One pipe fills a storage pool in 20 hours. a second pipe fills the same pool in 15 hours. when a third pipe is added and all three are used to fill the pool, it takes only 6 hours. find how long it takes the third pipe to do the job.

Answer 1

We work in rates per hour so we have the equation:-

1/20 + 1/15 + 1/x = 1/6 where x is the time for the third pipe

1/x = 1/6 - 1/15 - 1/20 = 1/20

so x = 20

The answer is 20 hours.