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                             Pipes and Cisterns   Quantitative Aptitude Questions – Pipes And Cisterns Solved Question 1 Two taps A ...

08.Aptitude Questions For Placement Papers -- PIPES AND CISTERNS Solved Problems

                             Pipes and Cisterns 

Quantitative Aptitude Questions – Pipes And Cisterns Solved Question 1
Two taps A and B can fill a tank in 15 minutes and 25 minutes respectively. If both the taps are opened simultaneously, in how many minutes the tank will be full?
a)9 3/5 minutes                  b)10 minutes                      c)12 minutes            d)18 minutes 
Answer: A
Explanation: In 1 minute, Tap A can fill =
1 / 15
th of the tank.
                    In 1 minute, Tap B can fill =
1 / 25
th of the tank.
    In 1 minute, both A and B can fill => A + B =
1 / 15
+
1 / 25
                                                                 =
(5+3) / 75
=
8 / 75
th of the tank
               Therefore, the tank will be full in
75 / 8
= 9
3 / 5
minutes      

Aptitude Questions with Solutions – Pipes and Cisterns Solved Question 2
A tap fills a tank in 15 minutes and the other empties it in 20 minutes. If both are opened simultaneously, then the tank will be filled in
a) 42 hours                       b) 20 hours                        c) 60 hours                  d) 22 hours        
Answer: C
Explanation: First pipe can fill the tank in 1 minute =
1 / 15
                   Second pipe can empty the tank in 1 minute =
1 / 20
              Both pipes fill the tank in 1 minute =
1 / 15
-
1 / 20
                                                              =     
(4-3) / 60
=
1 / 60
th of the tank
                   In 60 minutes, the tank will be full.

Quantitative Aptitude Study Material –Pipes and Cisterns Solved Problem 3
Two  pipes A and  B will fill the tank in 20 minutes  and 30 minutes and another leak pipe C empties water from the full tank in 40 minutes. If all the three are opened simultaneously the time taken to fill the tank is
a) 14 min                          b)17 1/7 minutes                          c)24 min          d)34 min        Answer : B
Explanation : In 1 minute , tap A can fill  =
1 / 20
th of the tank
                    In 1 minute, tap B can fill  =
1 / 30
th of the tank
                     In 1 minute, tap C can empty =
1 / 40
th of the tank
In 1 minute , if they all opened , they can fill => A+B –C =
1 / 20
+
1 / 30
-
1 / 40
ð  $\frac{6+4-3}{120}$   
ð  $\frac{7}{120}$ th of the tank
  If three pipes are opened simultaneously, in
120 / 7
= 17
1 / 7
minutes the tank will be filled.

Quantitative Aptitude Free Study Material – Pipes and Cisterns Solved Problem 4
A cistern is normally filled in 8 hours but takes 4 hours longer to fill because of a leak at its bottom. If the cistern is full, the time taken by the leak to empty the cistern is
a) 12 hours                     b)  20 hours                  c) 24 hours                   d) 30 hours
Answer:C
Explanation : Normally its takes 8 hours but it takes 4 hours longer because of the leak.
 So totally it takes 12 hours to fill the cistern.
Let the leak empties the tank in x hours.
In 1 hour, the cistern is filled
1 / 8
th and leaked in
1 / x
th.
  
1 / 12
=
1 / 8
1 / x
  => 
1 / x
=
1 / 8
  -
1 / 12
=
1 / 24
In 1 hours , the leak empties
1 / 24
th of the cistern.
If cistern is full, the time taken by the leak to empty the cistern is 24 hours.

Quantitative Reasoning for GRE  – Pipes and Cisterns Solved Problem 5
Two pipes P and Q can fill a tank in 15 minutes and 20 minutes respectively. An outlet R        can empty it in 10 minutes. If all the pipes are opened at 9 a.m. , the time at which
3 / 4
th part of the tank is filled is
a)9:05 am                     b)9:15 am                             c)9 : 45 am             d)10.10 am
Answer : C
Explanation : In 1 minute, P can fill
1 / 15
th of the tank
                                            Q can fill
1 / 20
th of the tank
                                        R can empty
1 / 10
th of the tank
If all the pipes all opened, in 1 minute, they can fill 
=> $\frac{1}{15} $+ $ \frac{1}{20}$- $ \frac{1}{10} $
=> $\frac{1}{60}$
In 60 minutes, the tank will be filled if all the pipes opened together.
To fill
3 / 4
th tank, it will take 45 minutes.
Therefore,
3 / 4
th of the tank is filled at 9: 45 am

Aptitude Questions with Explanations – Pipes and Cisterns Solved Problem 6
Two taps can separately fill a tank in 5 minutes and 10 minutes respectively.  If the taps are opened alternatively each for a minute then the time taken to fill the tank is
a) 6.5 minutes          b) 6 minutes                  c) 7.5minutes                       d) 4.5minutes
Answer: A
Explanation:  In 2 minutes Two taps can fill  =
1 / 5
+
1 / 10
=
3 / 10
th tank
                   Work of two pipes for 3 minutes each = 3 x
3 / 10
=
9 / 10
th tank will be filled
 ( 4 minutes of each one’s work exceeds1)
  Remaining part  of the tank to be filled = 1-
9 / 10
=
1 / 10
th of the tank
      Time taken by 1st tap to fill
1 / 10
of the tank =
1 / 10
x 5 =
1 / 2
minute
   Hence total time taken = (3 + 3) +
1 / 2
= 6.5 minutes

Aptitude Questions with Answers – Pipes and Cisterns Solved Questions 7
One pipe fills a tank three times faster than another pipe. If the two pipes together can fill the empty tank in 27 min, then how much time will the slower pipe alone take to fill the tank
a)90 minutes                      b)1 h 48 min                      c) 2 h            d) 2 h 24 min
Answer : B
Explanation : Let time taken by faster pipe be x minutes and  slower pipe takes 3x minutes.
In 1 minute , the both together =>
1 / x
+
1 / 3x
=
1 / 27
                                                =>
3+1 / 3x
=
1 / 27
                                                => x= 36
    Therefore , time taken by slower pipe is  3x = 3 x 36 = 108 minutes
                                                                             = 1 hour 48 minutes

Aptitude Questions with Explanations – Pipes and Cisterns Solved Problem 8
A cistern has two pipes. One can fill it with water in 7 hours and other can empty it in 5 hours. In how many hours will the cistern be emptied, if both the pipes are opened together when 5/7 of the cistern is already full of water?
a)12 hours                         b)12.5 hours                      c)14 hours               d)15 hours
Answer: B
Explanation:
When both pipes are opened, in 1 hour the tank emptied =
1 / 7
-
1 / 5
                                                                              =  
(5-7) / 35
  =
2 / 35
Therefore in 1 hour ,
2 / 35
th part of the tank is  emptied.
    Hence ,
5 / 7
is tank is already full.
To empty ,
5 / 7
th part of the tank =>
5 / 7
x
35 / 2
=12.5 hours
  
Aptitude Questions with Solutions  – Pipes and Cisterns Solved Problem 9
Sravani and Sameera together fill a cistern with water. Sravani pours 4 L of water every 3 min and Sameera pours 3 L every 4 min. How much time will it take to fill 200 L of water in the cistern?
a) 36 min                        b) 48 min                           c)72 min                 d)96 min
Answer : D
Explanation :
 In 3 minutes , Sravani can pour 4 lit =>In 1 minute , Sravani can fill
4 / 3
lit
 In 4 minutes ,Sameera can pour 3 lit => In 1 minute, Sameera can fill
3 / 4
lit
   Water filled by Sravani and Sameera in 1 min is =>
4 / 3
  +
3 / 4
=
25 / 12
lit         
      Time taken by them to fill 200 liters =  200 x
12 / 25
= 96 minutes
       
Aptitude Questions for GMAT and GRE  – Pipes and Cisterns Solved Problem 10
A tank is 3/5 th is full.  Pipe A can fill the tank in 20 minutes and the pipe B can empty it in 12 minutes. If both the pipes are open , h0w long will it take to empty or fill the tank completely ?
a)36 minutes           b)40 minutes                     c)18 minutes            d)24  minutes
Answer:   C
Explanation :
Here c , in 1minute, piple A can fill
1 / 20
th of the tank
            In 1 minute , piple B can empty 
1 / 12
th of the tank.
Part of the tank filled or emptied in 1 minute   A -B=
1 / 20
1 / 12
  
  = $ \frac{3-5}{60} $
  =-
1 / 30
We got negative value, therefore tank will be emptied. When the both pipes open simultaneously, the full tank will be emptied in 30 minutes
Thus,
3 / 5
th full of the tank will be emptied in =  30  x
3 / 5
= 18 minutes

Aptitude Questions with Explanations  – Pipes and Cisterns Solved Problem 11
Three-fourth of a tank is full of water. If 8 liters of water is added to it, then four-fifth of the tank becomes full. Find the capacity of the tank?
a)80 liters                          b)100 liters                        c)150 liters              d) 160 liters  
Answer: D
Explanation :   Let the capacity of the tank be x.
               
3 / 4
x + 8 =
4 / 5
x   
             = 
4x / 5
-
3x / 4
= 8
             = 
x / 20
= 8
Capacity of the tank = 160 Liters

Aptitude Questions for Competitive Exams – Pipes and Cisterns Solved Problem 12
A pipe can empty a tank in 60 minutes. A 2nd pipe with diameter thrice much as that of the first is also attached with the tank to empty it . The two pipes together can empty the tank in
a)8 minutes                       b)10 minutes                     c)12 minutes            d)15 minutes
Answer : D
Explanation :1st pipe can empty the tank in 60 minutes .
 Hence, 2nd pipe has thrice the diameter of 1st pipe , then it can empty tank in
1 / 3
of the time    => 60 x
1 / 3
= 20 minutes
In 1 minute, the both together can empty =.
1 / 60
+
1 / 20
=
1+3 / 60
=  
1 / 15
   Therefore, two pipes together can empty the tank in 15 minutes

Aptitude Questions for Placement Papers  – Pipes and Cisterns Solved Problem 13
Two pipes A and B can fill a tank in 12 min and 20 min, respectively. If both the pipes are opened simultaneously, after how much time should B be closed, so that the tank is full in 9 min?
a) 6 min                            b)12 min                           c) 8 min                  d)5 min
Answer : D
Explanation :
The 2nd taps is closed after some time , So first tap is worked for 9 minutes
           1n 9 minutes, first tap fills =>
1 / 12
x 9 =
3 / 4
of the tank
    So remaining ¼ th part of the tank is filled by B.
To fill ¼ th of the tank, B takes =>
1 / 4
x 20 = 5 minutes
   So after 5 minutes, B should be closed.

Quantitative Aptitude Questions   – Pipes and Cisterns Solved Problem 14
A pipe A can fill a tank in 10 minutes and another pipe B can drain 45 liters per minute. If the both the pipes are opened together, the tank is full in 40 minutes. What is the capacity of the tank ?
a)500 lit                            b)600 lit                            c)800 lit                  d)900 lit
Answer:B
Explanation :
        A can fill tank in 10 minutes and let B can empty it in x minutes. When they both opened together, the tank is full is 40 minutes.
            In 1 minute =>
1 / 10
1 / x
=
1 / 40
                      
       Leak in 1 minute =>
1 / x
=
1 / 10
-
1 / 40
  =>$\frac{1}{x}$ =    $ \frac{4-1}{40}$
  =>$ \frac{1}{x} $ = $\frac{3}{40} $
  Leak in 1 minutes is
3 / 40
th of the tank .But leak drains 45 liters per minute.
              Capacity of the tank = 45 x
40 / 3
= 600 liters

Aptitude Questions with Answers – Pipes and Cisterns Solved Problem 15
An inlet pipe can fill an tank in 5 minutes and an outlet pipe can empty the tank in 36 mnutes. How many additional number of outlet pipes of the same capacity are required to be opened , so that the tank never over flows?
a)4                                   b)5                        c)7                                  d)8
Answer : C
Explanation :  
Inlet pipe fills the tank in 5 minutes and outlet pipe empties the tank in 36 minutes.
  So inlet pipe is 36/5 = 7.2 times efficient than , ensure that the an outlet pipe.
Therefore , in order to tank never overflows , we will need total 8 outlet pipes.
   Already we have 1 outlet pipe , thus we need only (8-1) = 7 outlet pipes