This set of Aptitude Questions and Answers (MCQs) focuses on “Three Pipes”.
1. 3 pipes can fill a tank in 20 minutes when opened simultaneously. If the efficiency of the first pipe is 20% more than the combined efficiencies of the other two pipes, find the time taken by the first pipe to fill the tank.
a) 26.66 minutes
b) 36.66 minutes
c) 46.66 minutes
d) 56.66 minutes
View Answer
Explanation: Let the capacity of the tank be 20 liters.
The efficiency of all the pipes combined = 20 / 20 = 1
Let the efficiency of the last two pipes combined be x.
The efficiency of the first pipe = 20% more than x = 1.2x
The total efficiency of the pipes = 1.2x + x = 2.2x
2.2x = 1
X = 1 / 2.2
1.2x = 1.2 / 2.2 = 0.6 / 1.1
The time taken by the first pipe to fill the tank = 20 / (0.6 / 1.1) = 20 * 11 / 6 = 36.66 minutes.
2. 3 pipes have an efficiency of x, 2x and 7x. If the time taken by all the three pipes combined to fill a tank is 12.5 minutes, find the time taken by the second pipe to fill the tank.
a) 33.5 minutes
b) 55.5 minutes
c) 62.5 minutes
d) 89.5 minutes
View Answer
Explanation: The total time taken by the pipes combined to fill the tank = 12.5 minutes
Let the capacity of the tank be 12.5 liters.
The efficiencies of all the pipes combined = 1
10x = 1
X = 0.1
The efficiency of the second pipe = 2x = 0.2
12.5 / 0.2 = 62.5 minutes
3. 3 pipes can fill a tank in 5 minutes combined. If the first 2 pipes can fill the tank in 12 minutes combined, find the time required by the third pipe to fill the tank.
a) 8.27 minutes
b) 8.57 minutes
c) 8.77 minutes
d) 8.87 minutes
View Answer
Explanation: Let the capacity of the tank be 120 liters.
The efficiency of all pipes combined = 120 / 5 = 24
The efficiency of the first 2 pipes combined = 120 / 12 = 10
The efficiency of the third pipe = 24 – 10 = 14
The time taken by the third pipe to fill the tank = 120 / 14 = 8.57 minutes
4. 3 pipes can fill a tank in 8 minutes, 9 minutes and 10 minutes simultaneously. How long does it take to fill the tank by using only the first and the last pipe?
a) 2.22 minutes
b) 4.44 minutes
c) 6.66 minutes
d) 8.88 minutes
View Answer
Explanation: Let the capacity of the tank be 720 liters.
The efficiency of the pipes = 720 / 8, 720 / 9 and 720 / 10 respectively
The pipes in use = the first and last pipe
The relative efficiency in use = 90 + 72 = 162
The time taken by the pipes to fill the tank = 720 / 162 = 4.44 minutes
5. 3 pipes have an efficiency of x, 2x and 4x, respectively. Combined they can fill a tank in 35 minutes. If the first pipe is opened for 5 minutes, the second for 10 minutes and the third for 15 minutes, find the percentage of the tank filled.
a) 33.44%
b) 34.55%
c) 34.69%
d) 36.78%
View Answer
Explanation: The combined efficiency = x + 2x + 4x = 7x
The time taken by the pipes combined to fill the tank = 35 minutes
The capacity of the tanks = 35 * 7x = 245x liters
The amount of water filled in the tank as per the given conditions = x * 5 + 2x * 10 + 4x * 15 = 5x + 20x + 60x = 85x
The required percentage = 85x / 245x * 100 = 34.69%
6. 3 pipes can fill a tank in 3x, 5x and 8x minutes. If the tank is 240 liters in capacity, find the percentage of water which came from the second pipe.
a) 30.37%
b) 33.37%
c) 36.37%
d) 39.375
View Answer
Explanation: The capacity of the tank = 240 liters
The efficiency of the pipes 240 / 3x, 240 / 5x and 240 / 8x respectively.
The efficiency = 80 / x, 48 / x and 30 / x respectively
The efficiency is in a ratio 40 : 24 : 15
The percentage of water from the second pipe = 24 / 79 * 100 = 30.37%
7. 3 pipes can empty a semi filled tank in 4 minutes, 5 minutes and 6 minutes, respectively. If all the pipes are opened simultaneously, how long does it take to empty a filled tank?
a) 2.34 minutes
b) 2.43 minutes
c) 3.24 minutes
d) 3.42 minutes
View Answer
Explanation: The time taken by the 3 pipes to empty a fully filled tank = 8 minutes, 10 minutes and 12 minutes respectively.
Let the capacity of the tank be 120 liters.
The efficiency of the pipes = 120 / 8, 120 / 10 and 120 / 12 respectively = 15, 12, 10 respectively.
The relative efficiency = 15 + 12 + 10 = 37
The time required = 120 / 37 = 3.24 minutes
8. Out of 3 pipes 2 can empty a tank in 20 minutes and 25 minutes, respectively. If the third pipe can fill the tank in 10 minutes, find the time to fill the tank if all the pipes are opened simultaneously.
a) 20 minutes
b) 25 minutes
c) 50 minutes
d) 100 minutes
View Answer
Explanation: Let the capacity of the tank be 100 liters.
The efficiency of the pipes = 100 / 20, 100 / 25 and 100 / 10 respectively.
The relative efficiency = 10 – 5 – 4 = 1
The time taken = 100 / 1 = 100 minutes
9. Out of 3 pipes 2 can fill a tank in 4 minutes and 8 minutes simultaneously. If the third pipe can empty the tank in 12 minutes, find the time taken to fill the tank if all the pipes are opened simultaneously.
a) 3.48 minutes
b) 3.42 minutes
c) 3.44 minutes
d) 3.46 minutes
View Answer
Explanation: Let the capacity of the tank be 24 liters.
The efficiency of the pipes = 24 / 4, 24 / 8 and 24 / 12 = 6, 3, 2
The relative efficiency of the pipes = 6 + 3 – 2 = 7
The time required = 24 / 7 = 3.42 minutes
10. The time taken by 3 pipes to fill a tank is 10 minutes, 12 minutes and 14 minutes, respectively. If the first two pipes are opened simultaneously, find the time taken to fill the tank.
a) 4.54 minutes
b) 5.54 minutes
c) 4.45 minutes
d) 5.45 minutes
View Answer
Explanation: Let the tank be 120 liters in capacity.
The efficiency of the first two pipes = 120 / 10, 120 / 12 = 12, 10
The relative efficiency = 10 + 12 = 22
The time required = 120 / 22 = 5.45 minutes
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