Question

Two pipes can fill a cistern in 12 hours and 15 hours respectively. Due to leakage in the bottom,
30 minutes extra are taken for the cistern to be filled up if both the pipes are open together. If
the cistern is full, how much time will the leak take to empty the tank?​

Answer 1

Answer:

Cistern filled by both pipes in one hour = 1/12+1/20=2/15th

Therefore both pipes filled the cistern in 15/2hrs.

Now, due to leakage both pipes filled the cistern in 15/2+30/60=8hrs.

Therefore Due to leakage, filled part in one hour = 1/8

Therefore part of cistern emptied, due to leakage in one hour = 2/15-1/8= 1/120th

In 120 hrs, the leak would empty the cistern.

You can do like this