Learn and practice the chapter "Pipes and Cisterns" with these solved Aptitude Questions and Answers. Each question in the topic is accompanied by a clear and easy explanation, diagrams, formulae, shortcuts and tricks that help in understanding the concept.
Use of Pipes and Cisterns Questions
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1. I have two inlet pipes in my tank. Pipe P is diametrically bigger than Q and can fill a tank alone in 22 hours while Pipe Q takes 11 hours longer than Pipe P to fill the tank. If I open both the inlet pipes together, how long will they take to fill the tank?
a.
19
hours
22
b. 1
1
hours
11
c. 13
1
hours
5
d. 18 hours
Answer: c. 13
1
hours
5
Explanation:
Tank filled or work done by P in 1 hour =
1
22
Tank filled or work done by Q in 1 hour (Q takes 11 hrs more than P) =
1
33
Tank filled or work done by both pipes in 1 hour =
1
+
1
=
5
22
33
66
So the entire tank is full in
66
= 13
1
hours
5
5
Tip:
If A completes
1
amount of work in 1 day, he completes entire work in 'n' days.
n
2. Pipe A takes 38 hours to fill a tank alone while Pipe B takes half the time taken by Pipe A to fill the same tank alone. The leakage C can empty the entire tank in 133 hours. How many hours will it take to fill the tank if Pipe A and B are opened together and leakage C is also allowed to empty the tank simultaneously?
a. 14 hours
b. 19 hours
c. 28 hours
d. 95 hours
Answer: a. 14 hours
Explanation:
Tank filled by A in 1 hour =
1
38
Tank filled by B in 1 hour (A takes 38 hrs, so B would take 19 hrs) =
1
19
Tank emptied by leakage C in 1 hour =
1
133
Tank filled by all 3 openings together in 1 hour =
1
+
1

1
38
19
133
Making denominators common,
Tank filled by all 3 pipes together in 1 hour =
3.5
+
7

1
=
9.5
=
1
133
133
133
133
14
So the entire tank is full in
14
= 14 hours > Inverse or reciprocal of
1
1
14
3. Pipe A can fill a tank in 22.5 minutes while a diametrically bigger Pipe B can do it in 15 minutes. Initially we open both the pipes together for some time but after how much time, should we close Pipe B so that the tank is full in 18 minutes?
a. 2.5 minutes
b. 3 minutes
c. 4 minutes
d. 4.5 minutes
Answer: b. 3 minutes
Explanation:
A fills tank in 22.5 minutes and A remains open for 18 minutes  Given
So total tank filled by A = Tank filled in 1 min x 18 minutes =
1
x 18 =
4
22.5
5
This is the entire work done by A.
So whatever is the remaining work, it is done by only B
Let B be open for T minutes.
Total tank filled by B = 1 
4
=
1
= Tank filled in 1 min x T minutes =
1
x T
5
5
15
∴
1
=
1
x T
5
15
∴ T = 3 minutes = B should be closed after this much time
4. Pipe P can fill a cement tank in 24 hours. However, there is a leakage at the bottom of the tank due to which the Pipe P takes 12 hrs longer and fills it in 36 hours. How long would this leakage take to empty the entire tank?
a. 48 hours
b. 60 hours
c. 72 hours
d. 96 hours
Answer: c. 72 hours
Explanation:
Normally, Pipe P can fill the cement tank in 24 hours. So in 1 hour it fills =
1
part of tank
24
Due to leak, Pipe P can fill the tank in 36 hours. So in 1 hour it actually fills =
1
part of tub
36
∴ Water removed by the leak in 1 hour =
1

1
=
1
24
36
72
∴ Leak empties the tank in 72 hours.
5. Tap B is 5 times slower than Tap A in filling the same tank. Also tap B takes 32 minutes more than Tap A to fill the same tank completely. How long will the tank take to get full, if both the taps are opened simultaneously?
a.
5
minutes
32
b.
32
minutes
5
c.
20
minutes
3
d.
32
minutes
3
Answer: c.
20
minutes
3
Explanation:
Let Tap A take T minutes to fill the tank alone.
Since Tap A is 5 times faster than Tap B, Tap B takes 5 times more time.
So time taken by Tap B = 5T minutes
Also, 5TT = 32  Given
∴ T = 8 minutes = Time taken by A
Time taken by B = 5 x 8 = 40 minutes.