Arithmetic Aptitude :: Pipes & Cistern

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A cistern can be filled by a tap in 4 hours while it can be emptied by another tap in 9 hours. If both taps are opened simultaneously, then after how much time will the cistern get filled ?


A5 hours

B4.5 hours

C7.2 hours

D6.5 hours

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Answer: Option C

Explanation:

Time taken by tap A to fill the cistern=4 hrs
so work done by tap A in 1 hour = 1/4th
Time taken by tap B to empty the full cistern = 9 hours
so work done by tap B in 1 hour = 1/9th
=> Work done by (A + B) in 1 hour=(1/4 - 1/9)=5/36
Therefore, the tank will fill the cistern = 36/5 hours=7.2 hours.

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


A7 hours

B8 hours

C12 hours

D14 hours

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Answer: Option D

Explanation:

Work Done by the leak in 1 hrs = (1/2-3/7) = 1/14

so leak will empty the tank in 14 hrs.

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Pipe A can fill a tank in 8 hours and Pipe B can fill it in 6 hours. If both the pipes are opened but after 2 hours pipe A is closed, then the other pipe will fill the tank in


A6 hours

B3 1/2 hours

C4 hours

D2 1/2 hours

ENone of these

Answer: Option D

Explanation:

Tank part filled by Pipe A in 1 hour = 1/8
or
Time taken to fill 1/8 part of tank filled A = 1 hour ------------- (1)

Tank part filled by Pipe B in 1 hours = 1/6
or
Time taken to fill 1/6 part of tank filled B = 1 hour ---------(2)

=> Tank Part filled by (A+B) in 1 hour = (1/8 + 1/6)

=> Tank Part filled by (A+B) in 2 hour = 2*(1/8 + 1/6) = 2*(3+4)/24 = 2*7/24 = 7/12

After 2 hours left over portion of tank = (1-7/12) = 5/12

Time taken to fill 1/6 part of tank filled B = 1 hour
so time taken to fill 5/12 part of tank by B = 6 * 5/12 = 5/2 = 2 1/2
=> So it takes 2 1/2 hrs (2hrs 30 min) to fill 5/12 of tank.

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Choose the correct option.

Two pipes A and B can fill a tank in 9 hours and 3 hours respectively. If they are opened on alternate hours and if pipe A is opened first, in how many hours will the tank be full?


A4 hrs

B5 hrs

C2 hrs

D6hrs

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Answer: Option B

Explanation:

Tank part filled by pipe A in 1 hour =1/9
Tank part filled by pipe B in 1 hour =1/3

Given Pipe A and B are opened alternatively.

So Part filled in every 2 hours =(1/9+1/3)=4/9
Tank Part will be filled in 4 hour =2*4/9=8/9

Remaining part = (1-8/9)=1/9

So next is A turn.
So Pipe A will fill remaining 1/9 part in next 1 hour.

Total Time = (4 hrs + 1 hrs) = 5 hrs.

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A pump takes 8 hours to fill an overhead tank, but due to an open tap in the kitchen, the time taken is 10 hours. In how much time would the kitchen tap empty a full overhead tank?


A20 hours

B40 hours

C30 hours

D60 hours

Answer: Option B

Explanation:

Here is no explanation for this answer

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Pipe A can fill a cistern in 6 hours less than Pipe B. Both the pipes together can fill the cistern in 4 hours. How much time would A take to fill the cistern all by itself?


A1 hour

B2 hours

C6 hours

D8 hours

ENone of these

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Answer: Option C

Explanation:

Let's assume time required by Pipe A to fill the cistern = X hours
So Time required by Pipe B to fill the cistern = (X + 6) hours
? Both Pipes (A+B) can fill cistern in 1 hour = [1/X + 1/(X + 6)]
Given Both pipe fill the cistern in 4 hours
=> [1/X + 1/(X + 6)] = 1/4 => [(X+6) + X]/(X+6)*x = 1/4
4X + 24 + 4X = X2 + 6x
X2 - 2X - 24 = 0
(X-6)(X+4) = 0
=> A can fill cistern in 6 hours.

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Choose the correct option.

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?


A8

B15

C16

D18

Answer: Option D

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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One pipe can fill a tank three times as fast as another pipe. If together the two pipes can fill the tank in 36 min, then the slower alone will be able to fill the tank in:


A81 min

B108 min

C144 min

D192 min

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Answer: Option C

Explanation:

Lets assume time required by slower pipe alone to fill the tank = x minutes.
Then, faster pipe will fill it in x/3 minutes.
=> 1/x+3/x = 1/36
=>4/x = 1/36 => x = 144 min.

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Choose the correct option.

A tap supplies 8 litres of water per minute into a cistern. A leak at the bottom of the cistern can empty the cistern in 10 hours. A full tank with the tap open is emptied by the leak in 15 hours. What is the capacity of the tank?


A15000 litres

B12800 litres

C14400 litres

D13400 litres

ENone of these

Answer: Option C

Explanation:

Tank can be emptied by leak in 1 hour = 1/10
or
Time required to emptied 1/10 part of tank = 1 hour
Given full tank can be emptied by leak = 15 hours
or time need to emptied 1/15 part of tank by leak = 1 hours
so (1/10 - 1/15) part can be filled by tap = 1 hours
=> 1/30 part can be filled by tap = 1 hours
or
Time needed to fill the cistern by tap = 30 hours = 1800 minutes
so Capacity of cistern = 8 * 1800 = 14400 liters

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Two pipes A and B can fill a cistern in 20 and 30 minutes respectively, and a third pipe C can empty it in 40 minutes. How long will it take to fill the cistern if all the three are opened at the same time?


A19 1/7 min

B15 1/7 min

C17 1/7 min

D7 1/7 min

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Answer: Option C

Explanation:

Cistern part filled by pipe A in 1 min = 1/20
and by pipe B in 1 min = 1/30
Pipe C empty cistern in 1 min = 1/40 part.
When all pipes are open Cistern part will be filed = (1/20+1/30-1/40) = 7/120
=> Time required to fill the cistern = 120/7 = 17 1/7 min.

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