A cistern can be filled by a tap in 4 hours while it can be emptied by another tap in 9 hours. If both the taps are opened simultaneously, then after how much time will the cistern get filled?
Q1. A cistern can be filled by a tap in 4 hours while it can be emptied by another tap in 9 hours. If both the taps are opened simultaneously, then after how much time will the cistern get filled?
Answer: 7.2 hrs
Explanation: Net fill rate = 1/4 − 1/9 = 5/36 of the cistern per hour; time to fill = 36/5 = 7.2 hours.