Pipes and Cistern Aptitude Questions and Answers
This section focuses on "Pipes and Cistern" in Quantitative Aptitude. These Multiple Choice Questions (mcq) should be practiced to improve the Quantitative Aptitude skills required for various interviews (campus interviews, walk-in interviews, company interviews), placements, entrance exams and other competitive examinations.
1. A tube can fill a cistern in 18hrs.After half the cistern is filled, three more similar tubes are opened. What is
the total time taken to fill the cistern completely ?
Explanation: Time taken to fill the half cistern = 18/2 = 9 hrs
Remaining part = 1/2
Time taken to fill the remaining part = [1/(4×1/12)] ×(1/2) = 3/2hrs
3/2 hrs = 90 min = 1hr 30mints
Total time = 9hrs+90 min = 10hrs 30mins
2. Two taps can fill a tank in 4 hours and 5 hours .If two taps are operate simultaneously, In how much time
will the tank be filled ?
Explanation: 1/(A+B) =1/4 + 1/5
=>20/9=2hrs 13min to filled the tank
3. A pipe can fill the tank in 12 hours.Because of a leak in the tank it took 16(1/2) hours to fill the tank.If the
tank is full,how much time will the leak take to empty it?
Explanation: 1/12-2/33 = 11-4/132.
132/7 hrs=>1131 mins 18hrs 51min
4. One tap can fill a tank thrice as fast as another tap. If together the two taps can fill the tank in 12 minutes,
then the slower tap alone will be able to fill the tank in
3+1/3x = 4/3x = 1/12
3x = 48
5. Three taps P,Q,R can fill a bunker in 3 hrs. After working at it together for 1 hr, R is closed and P,Q can fill
the remaining part in 3 hrs. The number of hrs taken by R alone to fill the bunker.
Explanation: Part filled in 1 hr = 1/3
Remaining part = 1 – 1/3 = 2/3
(P + Q)'s 3 hours work = 2/3
(P+Q)'s 1 hour work = 2/9
R's 1 hr work = [(P+Q+R)'s 1 hr work – (P+Q)'s 1 hr work]
= 1/3 – 2/9 = 3-2/9 = 1/9
R alone can fill the tank in 9 hours.
6. An electric pump can fill a cistern in 6 hrs. Because of a leak in the cistern it took 7 hrs to fill the cistern. If
the cistern is full, how much time will the leak take to empty it?
Explanation: Work done by the leak in 1 hr = [1/6 – 1/7]
Therefore the leak will empty the cistern in 42 hrs.
7. A tank can be filled by a tap in 8 hrs while it can be emptied by another tap in 18 hrs. if both the taps are
opened simultaneously, then after how much time will the cistern get filled?
Explanation: Net part filled in 1hr = (1/8 – 1/18)
= 9 – (4/72)
Therefore the tank will be filled in 72/5 hrs i.e., 14 hrs 24mins
8. A dumper is filled in 15hrs by 3 tubes P,Q,and R. the tube R is thrice as fast as Q and Q is thrice as fast as P. How much time will tube Q alone take to fill the tank?
Explanation: Suppose tube P alone takes x hrs to fill the tank
Then tubes Q and R will take x/3 and x/9 hrs respectively to fill the dumper.
Therefore 1/x + 3/x+ 9/x = 1/15
13x = 1/15
X = 195 hrs
9. A tank can be filled by an inlet tap at the rate of 8 litres per minute. A leak in the bottom of a tank can
empty the full tank in 16 hours. When the tank is full, the inlet is opened and due to the leak, the tank is
empty in 80 hours. How many litres does the tank hold?
Explanation: Part emptied by the leak in 1 hour = 1/16
part filled by (leak & inlet open) in 1 hour = 1/80
Part filled by the inlet tap in 1 hour = 1/16 – 1/80 = 1/20
Inlet tap fills the tank in = 20 hours
Inlet tap fills water at the rate of 8 litres a minute.
Capacity of tank = 20 * 60 * 8= 9600 litre
10. Two faucet A and Bcan fill a cistern in 6 hours and 2 hours respectively. If they are opened on alternate
hours and if faucet A is opened first, in how many hours will the cistern be full?
Explanation: Faucet A can fill = 1/6
faucet B can fill = 1/2
For every two hour, 1/6 + 1/2 = 1+3/6
=>4/6=2/3 Part filled
Total filled in 3 hours = 2/3+1/6= 5/6
In next hour it will be fille full. So total time will be 4 hours.