Pipes and Cistern Questions

FACTS  AND  FORMULAE  FOR  PIPES  AND  CISTERN  QUESTIONS

 

 

1. Inlet : A pipe connected with a tank or a cistern or a reservoir, that fills it, is known as an inlet.

 

2. Outlet : A pipe connected with a tank or cistern or reservoir, emptying it, is known as an outlet.

 

(i) If a pipe can fill a tank in x hours, then:

part filled in 1 hour = 1/x

(ii) If a pipe can empty a tank in y hours, then:

part emptied in 1 hour = 1/y

(iii) If a pipe can fill a tank in x hours and another pipe can empty the full tank in y hours (where y > x), then on opening both the pipes, then the net part filled in 1 hour = 1x-1y

(iv) If a pipe can fill a tank in x hours and another pipe can empty the full tank in y hours (where x > y), then on opening both the pipes,  the net part emptied in 1 hour = 1y-1x

Q:

A water tank is two-fifth full.Pipe A can fill a tank in 10 minutes and pipe B can empty it in 6 minutes.If both the pipes are open,how long will it take to empty or fill the tank completely?

A) 6 min.to empty B) 6 min.to fill
C) 9 min.to empty D) 9 min.to fill
 
Answer & Explanation Answer: A) 6 min.to empty

Explanation:

Clearly,pipe B is faster than pipe A and so,the tank will be emptied.

 

part to be emptied = 2/5

 

part emptied by (A+B) in 1 minute=16-110=115

 

115:25::1:x

 

25*15=6mins

 

so, the tank will be emptied in 6 min

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126 93125
Q:

Two pipes A and B can fill a tank in 15 minutes and 20 minutes respectively. Both the pipes are opened together but after 4 minutes, pipe A is turned off. What is the total time required to fill the tank?

A) 10 min. 20 sec. B) 11 min. 45 sec.
C) 12 min. 30 sec. D) 14 min. 40 sec.
 
Answer & Explanation Answer: D) 14 min. 40 sec.

Explanation:

Part filled in 4 minutes =4(1/15+1/20) = 7/15

 

Remaining part =(1-7/15) = 8/15

 

Part filled by B in 1 minute =1/20 : 8/15 :: 1:x 

x = (8/15*1*20) = 1023min = 10min 40sec

The tank will be full in (4 min. + 10 min. + 40 sec.) = 14 min. 40 sec

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230 87563
Q:

A tap can fill a tank in 6 hours. After half the tank is filled, three more similar taps are opened. What is the total time taken to fill the tank completely?

A) 3 hrs 15 min B) 3 hrs 45 min
C) 4 hrs 15 min D) 4 hrs 1
 
Answer & Explanation Answer: B) 3 hrs 45 min

Explanation:

Time taken by one tap to fill half of the tank = 3 hrs.

 

  Part filled by the four taps in 1 hour =4*1/6 =2/3

 

Remaining part =1-12=12

 

23:12::1:x

 

=> x = 12*1*32=34

 

So, total time taken = 3 hrs. 45 mins.

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113 34428
Q:

A pump can fill a tank with water in 2 hours. Because of a leak, it took 213 hours to fill the tank. The leak can drain all the water of the tank in:

A) 7 hours B) 8 hours
C) 12 hours D) 14 hours
 
Answer & Explanation Answer: D) 14 hours

Explanation:

If the total area of pump=1 part

The pumop take 2 hrs to fill 1 part 

The pumop take1 hour to fill 1/2 portion 

 

Due to lickage  

The pumop take 7/3 hrs to fill 1 part 

The pumop take1 hour to fill 3/7 portion 

Now the difference of area = (1/2-3/7)=1/14 

 

This 1/14 part of water drains in 1 hour 

Total area=1 part of water drains in (1x14/1)hours= 14 hours 

 

So the leak can drain all the water of the tank in 14 hours. 

Leak will empty the tank in 14 hrs

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104 30734
Q:

Taps X and Y can fill a tank in 30 and 40 minutes respectively.Tap Z can empty the filled tank in 60 minutes.If all the three taps are kept open for one minute each,how much time will the taps take to fill the tank?

A) 48min B) 72min
C) 24min D) None of these
 
Answer & Explanation Answer: C) 24min

Explanation:

Given taps X and Y can fill the tank in 30 and 40 minutes respectively. Therefore,

 

part filled by tap X in 1 minute = 1/30

 

part filled by tap Y in 1 minute = 1/40

 

Tap Z can empty the tank in 60 minutes. Therefore,

 

part emptied by tap Z in 1 minute = 1/60

 

Net part filled by Pipes X,Y,Z together in 1 minute = [1/30 +1/40 - 1/60] = 5/120 = 1/24

 

i.e., the tank can be filled in 24 minutes.

 

 

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48 30058
Q:

A cistern is normally filled in 8 hours but takes two hours longer to fill because of a leak in its bottom. If the cistern is full, the leak will empty it in    ?

A) 20 hrs B) 28 hrs
C) 36 hrs D) 40 hrs
 
Answer & Explanation Answer: A) 20 hrs

Explanation:

1/8 - 1/x = 1/10

 => x = 40 hrs

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80 27527
Q:

A cistern has a leak which would empty the cistern in 20 minutes. A tap is turned on which admits 4 liters a minute into the cistern, and it is emptied in 24 minutes. How many liters does the cistern hold ?

A) 360 lit B) 480 lit
C) 320 lit D) 420 lit
 
Answer & Explanation Answer: B) 480 lit

Explanation:

1/k - 1/20 = -1/24

k = 120

120 x 4 = 480

Therefore, the capacity of the cistern is 480 liters.

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24 26981
Q:

A booster pump can be used for filling as well as for emptying a tank. The capacity of the tank is 2400  m3. The emptying capacity of the tank is 10 m3 per minute higher than its filling capacity and the pump needs 8 minutes lesser to empty the tank than it needs to fill it. What is the filling capacity of the pump?

A) 50 m^3/min B) 60 m^3/min
C) 72 m^3/min D) None of these
 
Answer & Explanation Answer: A) 50 m^3/min

Explanation:

Let the filling capacity of the pump be x m3/min. 

Then, emptying capacity of the pump=(x+10)m3/min.  

so,2400x-2400x+10=8 x2+10x-3000=0 

 

x-50+x+60=0 x=50

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