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 Pipes and Cistern Questions

Popular Latest Rated Important Formulae

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:

Two pipes can fill a tank in 20 and 24 minutes respectively and a waste pipe can empty 3 gallons per minute. All the three pipes working together can fill the tank in 15 minutes. The capacity of the tank is:

A) 60 gallons B) 100 gallons
C) 120 gallons D) 180 gallons
 
Answer & Explanation Answer: C) 120 gallons

Explanation:

Work done by the waste pipe in 1 minute =115-120+124=115-11120 = -140 [-ve sign means emptying]

 

Volume of 140part = 3 gallons

 

Volume of whole = (3 x 40) gallons = 120 gallons.

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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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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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Q:

A large tanker can be filled by two pipes A and B in 60 and 40 minutes respectively. How many minutes will it take to fill the tanker from empty state if B is used for half the time and A and B fill it together for the other half ?

A) 31 min B) 29 min
C) 28 min D) 30 min
 
Answer & Explanation Answer: D) 30 min

Explanation:

Part filled by (A + B) in 1 minute = (1/60 + 1/40) = 1/24
Suppose the tank is filled in x minutes.
Then, x/2(1/24 + 1/40) = 1
(x/2) * (1/15) = 1 => x = 30 min.

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Q:

12 buckets of water fill a tank when the capacity of each tank is 13.5 liters. How many buckets will be needed to fill the same tank,if the capacity of each bucket is 9 liters?

A) 8 B) 15
C) 16 D) 18
 
Answer & Explanation Answer: D) 18

Explanation:

Capacity of the tank =(12 x 13.5) liters =162 liters.

Capacity of each bucket =9 liters

Number of buckets needed = 162/9 =18.

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26 16941
Q:

Two pipes A and B can separately fill a cistern in 10 and 15 minutes respectively. A person opens both the pipes together when the cistern should have been was full he finds the waste pipe open. He then closes the waste pipe and in another 3 minutes the cistern was full. In what time can the waste pipe empty the cistern when fill  ?

A) 8.21 min B) 8 min
C) 8.57 min D) 8.49 min
 
Answer & Explanation Answer: C) 8.57 min

Explanation:

1/10 + 1/15 = 1/6 x 3 = 1/2

1 - 1/2 = 1/2

1/10 + 1/15 - 1/x = 1/2

x = 8.57 min

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Q:

One fill pipe A is 3 times faster than second fill pipe B and takes 32 minutes less than the fill pipe B. When will the cistern be full if both pipes are opened together?

A) 6 min B) 8 min
C) 12 min D) 10 min
 
Answer & Explanation Answer: C) 12 min

Explanation:

Let pipe A takes p min to fill

Then,

pipe B takes 3p min to fill

=> 3p - p = 32

=> p = 16 min => 3p = 48 min

 

Required, both pipes to fill = (48 x 16)/(48 + 16) min = 12 min.

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Q:

Pipe A can fill a tank in 16 minutes and pipe B cam empty it in 24 minutes. If both the pipes are opened together after how many minutes should pipe B be closed, so that the tank is filled in 30 minutes  ?

A) 21 min B) 24 min
C) 20 min D) 22 min
 
Answer & Explanation Answer: A) 21 min

Explanation:

Let the pipe B be closed after 'K' minutes.

30/16 - K/24 = 1 => K/24 = 30/16 - 1 = 14/16

=> K = 14/16 x 24 = 21 min.

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