Pipes and Cisterns Part 1

Problems on Pipes and Cisterns with Solutions Part 1

  1. Inlet:
    A pipe connected with a tank or a cistern or a reservoir, that fills it, is known as an inlet.
    Outlet:
    A pipe connected with a tank or cistern or reservoir, emptying it, is known as an outlet.
  2. If a pipe can fill a tank in x hours, then:
    part filled in 1 hour =1.
    x
  3. If a pipe can empty a tank in y hours, then:
    part emptied in 1 hour =1.
    y
  4. 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 =1-1.
    xy
  5. 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, then
    the net part emptied in 1 hour =1-1.
    yx
1. 
Three pipes A, B and C can fill a tank from empty to full in 30 minutes, 20 minutes, and 10 minutes respectively. When the tank is empty, all the three pipes are opened. A, B and C discharge chemical solutions P,Q and R respectively. What is the proportion of the solution R in the liquid in the tank after 3 minutes?
A.
5
11
B.
6
11
C.
7
11
D.
8
11
Answer: Option B
Explanation:
Part filled by (A + B + C) in 3 minutes = 31+1+1=3 x11=11.
3020106020
Part filled by C in 3 minutes =3.
10
 Required ratio =3x20=6.
101111
2. 
Pipes A and B can fill a tank in 5 and 6 hours respectively. Pipe C can empty it in 12 hours. If all the three pipes are opened together, then the tank will be filled in:
A.
113hours
17
B.
28hours
11
C.
39hours
17
D.
41hours
2
Answer: Option C
Explanation:
Net part filled in 1 hour1+1-1=17.
561260
 The tank will be full in60hours i.e., 39hours.
1717
3. 
A pump can fill a tank with water in 2 hours. Because of a leak, it took 2 hours to fill the tank. The leak can drain all the water of the tank in:
A.
41hours
3
B.7 hours
C.8 hours
D.14 hours
Answer: Option D
Explanation:
Work done by the leak in 1 hour =1-3=1.
2714
 Leak will empty the tank in 14 hrs.
4. 
Two pipes A and B can fill a cistern in 37 minutes and 45 minutes respectively. Both pipes are opened. The cistern will be filled in just half an hour, if the B is turned off after:
A.5 min.
B.9 min.
C.10 min.
D.15 min.
Answer: Option B
Explanation:
Let B be turned off after x minutes. Then,
Part filled by (A + B) in x min. + Part filled by A in (30 -x) min. = 1.
 x2+1+ (30 - x).2= 1
754575
11x+(60 -2x)= 1
22575
 11x + 180 - 6x = 225.
 x = 9.
5. 
A tank is filled by three pipes with uniform flow. The first two pipes operating simultaneously fill the tank in the same time during which the tank is filled by the third pipe alone. The second pipe fills the tank 5 hours faster than the first pipe and 4 hours slower than the third pipe. The time required by the first pipe is:
A.6 hours
B.10 hours
C.15 hours
D.30 hours
Answer: Option C
Explanation:
Suppose, first pipe alone takes x hours to fill the tank .
Then, second and third pipes will take (x -5) and (x - 9) hours respectively to fill the tank.
1+1=1
x(x - 5)(x - 9)
x - 5 + x=1
x(x - 5)(x - 9)
 (2x - 5)(x - 9) = x(x - 5)
 x2 - 18x + 45 = 0
(x - 15)(x - 3) = 0
 x = 15.    [neglecting x = 3]
6. 
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: Option C
Explanation:
Work done by the waste pipe in 1 minute =1-1+1
152024
    =1-11
15120
    = - 1.    [-ve sign means emptying]
40
 Volume of1part = 3 gallons.
40
Volume of whole = (3 x 40) gallons = 120 gallons.
7. 
A tank is filled in 5 hours by three pipes A, B and C. The pipe C is twice as fast as B and B is twice as fast as A. How much time will pipe A alone take to fill the tank?
A.20 hours
B.25 hours
C.35 hours
D.Cannot be determined
E.None of these
Answer: Option C
Explanation:
Suppose pipe A alone takes x hours to fill the tank.
Then, pipes B and C will takexandxhours respectively to fill the tank.
24
1+2+4=1
xxx5
7=1
x5
 x = 35 hrs.
8. 
Two pipes A and B together can fill a cistern in 4 hours. Had they been opened separately, then B would have taken 6 hours more than A to fill the cistern. How much time will be taken by A to fill the cistern separately?
A.1 hour
B.2 hours
C.6 hours
D.8 hours
Answer: Option C
Explanation:
Let the cistern be filled by pipe A alone in x hours.
Then, pipe B will fill it in (x + 6) hours.
1+1=1
x(x + 6)4
x + 6 + x=1
x(x + 6)4
 x2 - 2x - 24 = 0
 (x -6)(x + 4) = 0
 x = 6.     [neglecting the negative value of x]
9. 
Two pipes A and B can fill a tank in 20 and 30 minutes respectively. If both the pipes are used together, then how long will it take to fill the tank?
A.12 min
B.15 min
C.25 min
D.50 min
Answer: Option A
Explanation:
Part filled by A in 1 min =1.
20
Part filled by B in 1 min =1.
30
Part filled by (A + B) in 1 min =1+1=1.
203012
 Both pipes can fill the tank in 12 minutes.
10. 
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: Option D
Explanation:
Part filled in 4 minutes = 41+1=7.
152015
Remaining part =1 -7=8.
1515
Part filled by B in 1 minute =1
20
1:8:: 1 : x
2015
x =8x 1 x 20= 102min = 10 min. 40 sec.
153
 The tank will be full in (4 min. + 10 min. + 40 sec.) = 14 min. 40 sec.

1. 
One pipe can fill a tank three times as fast as another pipe. If together the two pipes can fill the tank in 36 minutes, then the slower pipe alone will be able to fill the tank in:
A.81 min.
B.108 min.
C.144 min.
D.192 min.
Answer: Option C
Explanation:
Let the slower pipe alone fill the tank in x minutes.
Then, faster pipe will fill it inxminutes.
3
1+3=1
xx36
4=1
x36
 x = 144 min.

12. 
A large tanker can be filled by two pipes A and B in 60 minutes 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.15 min
B.20 min
C.27.5 min
D.30 min
Answer: Option D
Explanation:
Part filled by (A + B) in 1 minute =1+1=1.
604024
Suppose the tank is filled in x minutes.
Then,x1+1= 1
22440
xx1= 1
215
 x = 30 min.

13. 
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
D.4 hrs 15 min
Answer: Option B
Explanation:
Time taken by one tap to fill half of the tank = 3 hrs.
Part filled by the four taps in 1 hour =4 x1=2.
63
Remaining part =1 -1=1.
22
2:1:: 1 : x
32
 x =1x 1 x3=3hours i.e., 45 mins.
224
So, total time taken = 3 hrs. 45 mins.

14. 
Three taps A, B and C can fill a tank in 12, 15 and 20 hours respectively. If A is open all the time and B and C are open for one hour each alternately, the tank will be full in:
A.6 hours
B.
62hours
3
C.7 hours
D.
71hours
2
Answer: Option C
Explanation:
(A + B)'s 1 hour's work =1+1=9=3.
12156020
(A + C)'s hour's work =1+1=8=2.
12206015
Part filled in 2 hrs =3+2=17.
201560
Part filled in 6 hrs =3 x17=17.
6020
Remaining part =1 -17=3.
2020
Now, it is the turn of A and B and3part is filled by A and B in 1 hour.
20
 Total time taken to fill the tank = (6 + 1) hrs = 7 hrs.

15. 
Three pipes A, B and C can fill a tank in 6 hours. After working at it together for 2 hours, C is closed and A and B can fill the remaining part in 7 hours. The number of hours taken by C alone to fill the tank is:
A.10
B.12
C.14
D.16
Answer: Option C
Explanation:
Part filled in 2 hours =2=1
63
Remaining part =1 -1=2.
33
 (A + B)'s 7 hour's work =2
3
(A + B)'s 1 hour's work =2
21
 C's 1 hour's work = { (A + B + C)'s 1 hour's work } - { (A + B)'s 1 hour's work }
   =1-2=1
62114
 C alone can fill the tank in 14 hours.

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