PlacementPrepPipe A fills a tank in 8 hours and pipe B fills it in 24 hours. How long will both together take to fill it?
Solution
Together per hour: 1/8 + 1/24 = 1/6 of the tank.
Time = 6 hours.
Answer: (B) 6 hours
Quantitative Aptitude · Work and motion
Pipes and Cisterns: placement practice questions
30 moderate questions in the pattern of campus placement tests. Pick an option to check your answer, then open the step-by-step solution.
A pipe can fill a tank in 8 hours. Because of a leak at the bottom, it takes 40 hours. In how long can the leak empty the full tank?
Solution
Filling with the leak, the tank fills 1/40 per hour; the pipe alone fills 1/8.
Leak per hour = 1/8 − 1/40 = 0.1, so the leak empties it in 10 hours.
Answer: (B) 10 hours
Pipes A and B fill a tank in 10 and 12 hours; pipe C empties it in 30 hours. If all three are opened together, how long will the tank take to fill?
Solution
Net per hour = 1/10 + 1/12 − 1/30 = 0.15.
Time = 6 2/3 hours.
Answer: (D) 6 2/3 hours
Pipes A and B can fill a tank in 10 and 15 hours. Both are opened, and after 3 hours B is closed. How much longer will A take to fill the tank?
Solution
In 3 hours both fill 0.5.
Remaining 0.5 is filled by A in 0.5 × 10 = 5 hours.
Answer: (A) 5 hours
A tap fills a tank at 8 litres per minute and a leak drains it at 3 litres per minute. The tank is full in 8 hours. What is its capacity?
Solution
Net filling = 8 − 3 = 5 L/min.
Capacity = 5 × 60 × 8 = 2400 L.
Answer: (B) 2400 litres
Pipe A fills a tank in 30 hours and pipe B fills it in 6 hours. How long will both together take to fill it?
Solution
Together per hour: 1/30 + 1/6 = 0.2 of the tank.
Time = 5 hours.
Answer: (D) 5 hours
Pipes A and B fill a tank in 12 and 30 hours; pipe C empties it in 24 hours. If all three are opened together, how long will the tank take to fill?
Solution
Net per hour = 1/12 + 1/30 − 1/24 = 3/40.
Time = 13 1/3 hours.
Answer: (A) 13 1/3 hours
Pipes A and B can fill a tank in 20 and 10 hours. Both are opened, and after 4 hours B is closed. How much longer will A take to fill the tank?
Solution
In 4 hours both fill 0.6.
Remaining 0.4 is filled by A in 0.4 × 20 = 8 hours.
Answer: (B) 8 hours
A tap fills a tank at 10 litres per minute and a leak drains it at 3 litres per minute. The tank is full in 8 hours. What is its capacity?
Solution
Net filling = 10 − 3 = 7 L/min.
Capacity = 7 × 60 × 8 = 3360 L.
Answer: (C) 3360 litres
Pipe A fills a tank in 6 hours and pipe B fills it in 12 hours. How long will both together take to fill it?
Solution
Together per hour: 1/6 + 1/12 = 0.25 of the tank.
Time = 4 hours.
Answer: (B) 4 hours
A pipe can fill a tank in 5 hours. Because of a leak at the bottom, it takes 7.5 hours. In how long can the leak empty the full tank?
Solution
Filling with the leak, the tank fills 2/15 per hour; the pipe alone fills 1/5.
Leak per hour = 1/5 − 2/15 = 1/15, so the leak empties it in 15 hours.
Answer: (D) 15 hours
Pipes A and B fill a tank in 12 and 15 hours; pipe C empties it in 15 hours. If all three are opened together, how long will the tank take to fill?
Solution
Net per hour = 1/12 + 1/15 − 1/15 = 1/12.
Time = 12 hours.
Answer: (A) 12 hours
A tap fills a tank at 5 litres per minute and a leak drains it at 2 litres per minute. The tank is full in 6 hours. What is its capacity?
Solution
Net filling = 5 − 2 = 3 L/min.
Capacity = 3 × 60 × 6 = 1080 L.
Answer: (C) 1080 litres
A pipe can fill a tank in 4 hours. Because of a leak at the bottom, it takes 5 hours. In how long can the leak empty the full tank?
Solution
Filling with the leak, the tank fills 0.2 per hour; the pipe alone fills 1/4.
Leak per hour = 1/4 − 0.2 = 0.05, so the leak empties it in 20 hours.
Answer: (A) 20 hours
Pipes A and B can fill a tank in 18 and 12 hours. Both are opened, and after 3 hours B is closed. How much longer will A take to fill the tank?
Solution
In 3 hours both fill 5/12.
Remaining 7/12 is filled by A in 7/12 × 18 = 10.5 hours.
Answer: (D) 10.5 hours
A tap fills a tank at 6 litres per minute and a leak drains it at 3 litres per minute. The tank is full in 6 hours. What is its capacity?
Solution
Net filling = 6 − 3 = 3 L/min.
Capacity = 3 × 60 × 6 = 1080 L.
Answer: (B) 1080 litres
A pipe can fill a tank in 5 hours. Because of a leak at the bottom, it takes 13 1/3 hours. In how long can the leak empty the full tank?
Solution
Filling with the leak, the tank fills 3/40 per hour; the pipe alone fills 1/5.
Leak per hour = 1/5 − 3/40 = 0.125, so the leak empties it in 8 hours.
Answer: (A) 8 hours
Pipes A and B fill a tank in 20 and 15 hours; pipe C empties it in 12 hours. If all three are opened together, how long will the tank take to fill?
Solution
Net per hour = 1/20 + 1/15 − 1/12 = 1/30.
Time = 30 hours.
Answer: (B) 30 hours
Pipes A and B can fill a tank in 15 and 30 hours. Both are opened, and after 4 hours B is closed. How much longer will A take to fill the tank?
Solution
In 4 hours both fill 0.4.
Remaining 0.6 is filled by A in 0.6 × 15 = 9 hours.
Answer: (B) 9 hours
A tap fills a tank at 8 litres per minute and a leak drains it at 2 litres per minute. The tank is full in 8 hours. What is its capacity?
Solution
Net filling = 8 − 2 = 6 L/min.
Capacity = 6 × 60 × 8 = 2880 L.
Answer: (B) 2880 litres
A pipe can fill a tank in 8 hours. Because of a leak at the bottom, it takes 13 1/3 hours. In how long can the leak empty the full tank?
Solution
Filling with the leak, the tank fills 3/40 per hour; the pipe alone fills 1/8.
Leak per hour = 1/8 − 3/40 = 0.05, so the leak empties it in 20 hours.
Answer: (C) 20 hours
Pipes A and B fill a tank in 30 and 15 hours; pipe C empties it in 20 hours. If all three are opened together, how long will the tank take to fill?
Solution
Net per hour = 1/30 + 1/15 − 1/20 = 0.05.
Time = 20 hours.
Answer: (D) 20 hours
Pipes A and B can fill a tank in 24 and 12 hours. Both are opened, and after 4 hours B is closed. How much longer will A take to fill the tank?
Solution
In 4 hours both fill 0.5.
Remaining 0.5 is filled by A in 0.5 × 24 = 12 hours.
Answer: (B) 12 hours
A tap fills a tank at 8 litres per minute and a leak drains it at 3 litres per minute. The tank is full in 12 hours. What is its capacity?
Solution
Net filling = 8 − 3 = 5 L/min.
Capacity = 5 × 60 × 12 = 3600 L.
Answer: (A) 3600 litres
A pipe can fill a tank in 6 hours. Because of a leak at the bottom, it takes 24 hours. In how long can the leak empty the full tank?
Solution
Filling with the leak, the tank fills 1/24 per hour; the pipe alone fills 1/6.
Leak per hour = 1/6 − 1/24 = 0.125, so the leak empties it in 8 hours.
Answer: (C) 8 hours
Pipes A and B fill a tank in 30 and 15 hours; pipe C empties it in 30 hours. If all three are opened together, how long will the tank take to fill?
Solution
Net per hour = 1/30 + 1/15 − 1/30 = 1/15.
Time = 15 hours.
Answer: (B) 15 hours
A tap fills a tank at 5 litres per minute and a leak drains it at 2 litres per minute. The tank is full in 8 hours. What is its capacity?
Solution
Net filling = 5 − 2 = 3 L/min.
Capacity = 3 × 60 × 8 = 1440 L.
Answer: (D) 1440 litres
Pipes A and B fill a tank in 15 and 20 hours; pipe C empties it in 60 hours. If all three are opened together, how long will the tank take to fill?
Solution
Net per hour = 1/15 + 1/20 − 1/60 = 0.1.
Time = 10 hours.
Answer: (D) 10 hours
Pipes A and B can fill a tank in 30 and 10 hours. Both are opened, and after 2 hours B is closed. How much longer will A take to fill the tank?
Solution
In 2 hours both fill 4/15.
Remaining 11/15 is filled by A in 11/15 × 30 = 22 hours.
Answer: (A) 22 hours
Pipe A fills a tank in 20 hours and pipe B fills it in 12 hours. How long will both together take to fill it?
Solution
Together per hour: 1/20 + 1/12 = 2/15 of the tank.
Time = 7.5 hours.
Answer: (B) 7.5 hours
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