# Pipes and Cisterns Questions and Answers

## Pipes and Cisterns Aptitude Questions

On this page we will be discussing about Pipes And Cistern Questions that are generally asked in placement Exams. Pipes and Cistern is a common topic asked in various companies exams. Two basic terminologies in Pipes and Cistern Topic are:

### Rules for Pipes and Cisterns

• Inlet is referred to as the pipe which is supposed to fill the tank.
• A pipe that is meant to empty the tank is called as outlet.
• When a pipe works for x hours for filling up the cistern, then 1/x portion of the cistern will be completed in 1 hour.
• When a pipe works for y hours to empty the cistern, then the portion of the cistern emptied in 1 hour is equals to
= $\frac{1}{y}$
• Pipe A might fill a cistern n times as quickly as another pipe B. This states that if slower pipe B works for x min to fill the empty tank,
then quicker pipe A works for x/n min to fill up the empty cistern. If they work collaboratively, then the portion of the cistern which is loaded up in 1 hour is
=$\frac{n+1}{x}$
• In some scenarios the efficiency of the pipes would have been given such as in percentage, to find the actual rate multiply the efficiency percentage with rate.
• Be very careful when using Units make sure all the units are same, or else answer might get wrong.

## Formulas to keep in mind.

Time, Rate, and Volume Relationship:
Time = Volume / Rate
Rate = Volume / Time
Volume = Rate × Time

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1. There are 15 vessels of water with the volume of 60 litters each. Together they can fill the cistern completely. Calculate how many vessels will be required to completely fill the cistern if their volume is reduced to 20 liters.

40 vessels

40 vessels

11.54%

45 vessels

45 vessels

79.95%

42 vessels

42 vessels

3.3%

35 vessels

35 vessels

5.22%

Solution:

Total capacity of cistern = 60*15 = 900 liters

Total vessels needed to fill the cistern if the total volume of each vessel is reduces to 20 liters = 60*15 / 20 = 900/20 = 45 vessels

2. There are two pipes, Pipe M and Pipe N. They can fill a container respectively in 9 hours and 3 hours. Both Pipe M and Pipe N are opened alternatively in every hour and pipe N is started after pipe M. Identify in how many hours the container will be overflowed?

7 hr

7 hr

8.88%

5 hr

5 hr

64.5%

6 hr

6 hr

12.13%

4 hr

4 hr

14.5%

Solution:

Container filled by pipe M in 1 hour = 1 / 9

Container filled by pipe N in 1 hour = 1 / 3

Container filled by both if open alternatively = 1/9 + 1/3 = 4/9 (in 2 hours)

Container filled by both in another 2 hours = 4/9 + 4/9 = 8/9

Remaining 1/9th part will be filled by pipe M in another one hour.

Total time = 2+2+1 = 5 hours

3. An electric pump is used for emptying and filling a storage chamber of water. The storage chamber contains 3200 liters of water. What is the filling capacity, if the emptying of the storage chamber is 20 liters/minute more than its filling capacity and the pump requires 8 minutes less to empty the storage chamber than it requires to fill it?

100

100

14.22%

80

80

75.69%

70

70

5.96%

50

50

4.13%

Solution:

Let us assume the filling capacity of the pump be x liter/minute

The emptying capacity will be 20+x liter/minute

Time needed to fill the storage chamber = 3200 / x

Time needed to empty the storage chamber = 3200 / x+20

Given, the pump requires 8 minutes less in emptying the storage chamber,

= 3200/x – 3200/x+20 = 8

= 400/x – 400/x+20 = 1

= 400(x+20) – 400x = x(x+20)

= 400x + 8000 – 400x = x2 + 20x

= 8000 = x2 + 20x

= x2 + 20x – 8000 = 0

= (x +  100) (x - 80) = 0

x = -100, x = 80

Since liters cannot be negative, therefore the filling capacity is 80 liters/ minute.

4. Pipes A and B running together can fill a cistern in 6 minutes. If B takes 5 minutes more than A to fill the cistern, then what will be the respective times in which A and B will fill the cistern separately?

10 min and 12 minutes

10 min and 12 minutes

10.74%

10 min and 15 minutes

10 min and 15 minutes

79.75%

20 min and 10 minutes

20 min and 10 minutes

4.96%

16 min and 11 minutes

16 min and 11 minutes

4.55%

## Suppose pipe A fills the cistern in x min.

Therefore pipe B will fill the cistern in  min
In one minute, pipe A and B can together fill  part of the cistern
Given 1/

Neglecting negative values
A and B will fill the cistern separately in 10 min and 15 min

5. Due to an open outlet pipe a tank will tank 4 hours more to be filled. Normally it takes 8 hours to completely fill. How many hours the outlet pipe will take to empty the full tank?

20 hrs

20 hrs

9.91%

24 hrs

24 hrs

78.83%

18 hrs

18 hrs

9.01%

19 hrs

19 hrs

2.25%

Solution:

The complete tank is filled in 8 hours, so in 1 hour = 1/8th tank will be filled

Due to outlet pipe in 1 hour = 1/12th part will be filled

Part of the tank emptied in 1 hour = 1/8 – 1/12 = 1/24

Therefore the tank will be emptied in 24 hours.

6. A pipe normally fill a cistern in four hours less than 24 hours. Because of a crack on one side of the cistern the pipe will take 5 hours more to fill. If the cistern is completely filled, in how much time the leakage will completely unfill the cistern?

100 hrs

100 hrs

80.35%

110 hrs

110 hrs

8.3%

120 hrs

120 hrs

6.99%

125 hrs

125 hrs

4.37%

Solution:

The cistern is filled in 20 hours

In 1 hour = 1/20th portion of the cistern is filled

Due to crack the cistern is filled in 25 hours

In 1 hour = 1/25th portion of the cistern is filled

Part of the tank emptied in a hour = 1/20 – 1/25 = 1/100

Therefore, the cistern will be completely unfilled in 100 hours.

7. A tank is 250m in length and 200m in breadth. It is filled through a pipe 0.5m long and 0.4m wide at a speed of 25km/hour. In how much time the water in the tank will reach to 18m level?

110

110

9.7%

160

160

19.39%

180

180

64.24%

140

140

6.67%

Solution:

25 km = 25*1000 = 25000 m

In 1 hour the level of the water will be = 0.5*0.4*25000 = 5000m3

Let us assume that, in x hours the water level will reach to 18m.

Therefore, 5000x = 250×200×18

5000x = 180 hours.

8. In 40 minutes Pipe R can fill a tanker completely. The same tanker can be filled by Pipe Q 5 times faster than pipe R. In how much time both the pipe together can fill the tanker?

25 minutes

25 minutes

8.98%

20 minutes

20 minutes

22.75%

15 minutes

15 minutes

10.18%

10 minutes

10 minutes

58.08%

Solution:

Pipe R fills the tanker in 40 mins

Pipe R will fill the tanker in 1 minute = 1/40th of the tank

Pipe Q fills the tank in 5/40 = 8 minutes

Pipe Q will fill the tanker in 1 minute = 1/8th of the tank

Together they can fill the tanker in a single minute = (1/8) – (1/40) = 1/10th part

Therefore, the tanker will be filled in 10 minutes.

9. There is a leakage in the bottom of the tank. Because of it, the tank will take 7 hours more to 14 hours. Find out the time the leakage will take to completely empty the tank?

24 hrs

24 hrs

9.18%

30 hrs

30 hrs

6.63%

22 hrs

22 hrs

7.14%

42 hrs

42 hrs

77.04%

Solution:

Let us assume the leakage will take x hours to empty the tank

Then, 1/x = 1/21 – 1/14

1/x = 1/42

Therefore x = 42 hours.

10. Pipe A is 4 times faster than Pipe C. Together they can fill a cistern in 42 minutes. Calculate the time taken by slower pipe to alone fill the cistern?

140

140

9.5%

150

150

10.5%

200

200

5%

210

210

75%

Solution:

Let us assume the time taken by slower pipe as x

Then, the time taken by faster pipe = x/4 minutes.

Given, 1/x + 4/x = 1/42

5/x = 1/42

x = 210 minutes

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