Pipes and cisterns topic is similar to time and work. A pipe is connected to a tank or cistern. It is used to fill or empty the tank; accordingly it is called an inlet (or) an outlet. Inlet pipe: A pipe that fills a tank or cistern is the inlet pipe. Outlet pipe: A pipe that empties a tank or cistern is the outlet pipe.
Model Questions
1. Two pipes can separately fill a tank in 20 min and 30 min respectively. If both pipes are opened simultaneously, then how long will it take to fill the tank?
1) 6 min 2) 8 min 3) 10 min
4) 12 min 5) 15 min
Sol:
Ans: 4
2. Two pipes A and B can fill a tank independently in 16 hours and 24 hours respectively. 3 If the tank is already 
full and both the 8 pipes are opened simultaneously, in how much time they can (functioning together) fill the remaining tank? (in hours)
1) 6 2) 8 3) 10 4) 4 5) 12
Sol:
Ans: 1
3. Two pipes can fill a tank in 12 hours and 18 hours respectively. A third pipe can empty the tank in 72 hours. If all the three pipes are opened and function simultaneously, then in how much time the tank will be full? (in hours)
1) 15 2) 6 3) 12 4) 8 5) 16
Sol:
Ans: 4
4. Two pipes can fill a tank in 12 min and 15 min, respectively and waste pipe can empty10 liters per min. All the three pipes working together can full the tank in 1 hour. Find the capacity of the tank.
1) 75 lt 2) 120 lt 3) 90 lt
4) 180 lt 5) 150 lt
Sol:
Ans: 1
5. A tank has a leak which would empty it in 8 hours. A tap is turned on which admits 5 lt a min into the tank and it is now emptied in 10 h. How many liters does the tank hold?
1) 24000 lt 2) 12000 lt 3) 18000 lt
4) 16000 lt 5) 14000 lt
Sol:
Ans: 2
6. One pipe can fill a tank four times as fast as another pipe. If together the two pipes can fill the tank in 36 minutes, then the slower pipe alone will be able to fill the tank in.......
1) 180 min 2) 136 min 3) 126 min
4) 114 min 5) 145 min
Sol:
Ans: 1
7. Two pipes A and B together can fill a cistern in 4 hours. Had they been opened separately, then B would have taken 6 hours more than A to fill the cistern. How much time will be taken by A to fill the cistern separately?
1) 6 hrs 2) 2 hrs 3) 4 hrs
4) 3 hrs 5) 8 hrs
Sol:
Ans: 1
8. Two taps x and y can fill a tank in 24 min and 32 min respectively. Both the taps are opened simultaneously, after how many minutes y should be closed so that the tank is just filled in 18 min?
1) 6 min 2) 8 min 3) 9 min
4) 10 min 5) 4 min
Sol:
Ans: 2
9. Two taps, A and B can fill a tank (of capacity 210 litres) in 24 hours and 14 hours respectively. If both the taps are opened simultaneously and after 4 hours both the taps are closed, what quantity of water is to be added to the tank to fill it completely? (in litres)
1) 112 2) 132 3) 115 4) 125 5) 136
Sol:
Ans: 3
10. A cistern has three pipes A, B and C. Pipes A and B can fill it in 6 and 4 h respectively, while pipe C can empty the completely filled cistern in 2 h. If the pipes are opened in order at 3:00 pm, 4:00 pm and 5:00 pm, respectively, at what time will the cistern be empty?
1) 12:00 am 2) 11:00 pm 3) 1:00 am
4) 12:00 pm 5) 10:00 am
Sol:
Ans: 1
11. There are two inlets A and B connected to a tank. A and B can fill the tank in 10 h and 12 h, respectively. If both the pipes are opened alternately for 1 h, starting from A, then how much time will the tank take to be filled?
Sol:
Ans: 3
12. Two pipes P and Q can fill a tank in 16 minutes and 24 minutes respectively. Pipe P was opened for 4 minutes. After that, it was closed and pipe Q was opened for 8 minutes. After 12 minutes, both pipes were opened. Then in how much time the tank will be full?
1) 12 min 2) 16 min 3) 17.6 min
4) 12.5 min 5) 14.5 min
Sol:
Ans: 2
13. A water tank has one inlet A and one outlet B. A takes 8 hours to fill the empty tank, when B is not open and B takes 10 hours to empty the full tank. If the tank is three- fifth full, how much time will it take to fill the tank completely when both A and B are opened simultaneously? (in hours)
Sol:
Ans: 4
14. One fill pipe A takes 3 minutes more to fill the cistern than two fill pipes A and B opened together to fill it. Second fill pipe B takes 
minutes more to fill cistern than two fill pipes A and B opened together to fill it. When will the cistern be full if both pipes are opened simultaneously?
1) 7 minutes 2) 16 minutes
3) 8 minutes 4) 10 minutes
5) 12 minutes
Sol:
Ans: 3
