A pipe can fill a cistern in 20 minutes whereas the cistern when fill can be emptied by a leak in 28 minutes. When both pipes are opened, find when the cistern will be full?
Q1. A pipe can fill a cistern in 20 minutes whereas the cistern when fill can be emptied by a leak in 28 minutes. When both pipes are opened, find when the cistern will be full?
Answer: 70 min
Explanation: Net fill rate = 1/20 − 1/28 = (7−5)/140 = 1/70 of the cistern per minute; time to fill = 70 minutes.