Question

One pipe fills a storage pool in 15 hours. A second pipe fills the same pool in 5 hours. When a third pipe is added and all three are used to fill the​ pool, it takes only 3 hours. Find how long it takes the third pipe to do the job.

Answer 1

Given:

time taken by first pipe = 15 hours

time taken by second pipe = 5 hours

time taken by all three pipes together = 3 hours

Solution:

work rates of pipes are :

1st pipe = 1/15

2nd pipe = 1/5

3rd pipe = 1/x

all together = 1/3

sum of individual rates = rate when all pipes are working together

1/15 + 1/5 + 1/x = 1/3

1/x = 1/3 - 1/15 - 1/5

solving the equation, we get
1/x = 1/ 15

x= 15

hence, it would take 15 hours for the third pipe to fill the tank.