Pipes & Cistern
Important Instructions
Two pipes A and B can fill a tank in 12 and 24 minutes respectively. If both the pipes are used together, how long will it take to fill the tank?
Answer: B
Tank can be filled by pipe A in 12 minutes and pipe B in 24minutes.
=> Part filled by A in 1 minute= 1/12
=> Part filled by B in 1 minute= 1/24
=> Part filled by both in 1 minute= 1/12 + 1/24
= 3/24=1/8
Time taken to fill the entire tank = 8 minutes
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Two taps A and B can fill a tank in 10 hours and 15 hours respectively. If both the taps are opened together, the tank will be full in ?
Answer: B
If A can do a piece of work in x hours and B can do a piece of work in y hours.
Then A and B together will do the work in = 1/x+1/y
Time taken by A = 10 hours
Time taken by B = 15 hours
Time taken by A and B = (15×10 / 15+10) = 6 hours.
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A pipe can fill a tank in 6 hours. Another pipe can empty the tank in 12 hours. If both pipes are opened simultaneously, the part of tank filled by both pipes in 1 hour is?
Answer: C
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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?
Answer: A
| 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 | . |
| 20 | 30 | 12 |
Both pipes can fill the tank in 12 minutes.
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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?
Answer: B
Time taken by one tap to fill half of the tank = 3 hrs.
| Part filled by the four taps in 1 hour = | |
4 x | 1 | |
= | 2 | . |
| 6 | 3 |
| Remaining part = | |
1 - | 1 | |
= | 1 | . |
| 2 | 2 |
|
2 | : | 1 | :: 1 : x |
| 3 | 2 |
 x = |
|
1 | x 1 x | 3 | |
= | 3 | hours i.e., 45 mins. |
| 2 | 2 | 4 |
So, total time taken = 3 hrs. 45 mins.
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Two pipes A and B can fill a tank in 6 hrs and 4 Hrs respectively. If they are opened on alternate hrs and Pipe A is opened first, in how many hours shall the tank be full ..?
Answer: C
No answer description available for this question.
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Three pipes A, B and C were opened to fill a tank. Working alone, A, B and C require 10, 15 and 20 hours respectively. A was opened at 7 AM, B at 8 AM and C at 9 AM. At what time the tank would be completely filled, given that pipe C can only work for 3 hours at a stretch, and needs 1 hour standing time to work again.
Answer: B
Let the capacity of the tank be LCM (10, 15, 20) = 60
=> Efficiency of pipe A = 60 / 10 = 6 units / hour
=> Efficiency of pipe B = 60 / 15 = 4 units / hour
=> Efficiency of pipe C = 60 / 20 = 3 units / hour
=> Combined efficiency of all three pipes = 13 units / hour
Till 9 AM, A works for 2 hours and B work for 1 hour.
=> Tank filled in 2 hours by A = 12 units
=> Tank filled in 1 hour by B = 4 units
=> Tank filled till 9 AM = 16 units
=> Tank still empty = 60 – 16 = 44 units
Now, all three pipes work for 3 hours with the efficiency of 13 units / hour.
=> Tank filled in 3 more hours = 39 units
=> Tank filled till 12 PM = 16 + 39 units = 55 units
=> Tank empty = 60 – 55 = 5 units
Now, C is closed for 1 hour and these remaining 5 units would be filled by A and B working together with the efficiency 10 units / hour.
=> Time taken to fill these remaining 5 units = 5 / 10 = 0.5 hours
Therefore, time at which the tank will be completely filled = 12 PM + 0.5 hours = 12 : 30 PM
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Two pipes A and B work alternatively with a third pipe C to fill a swimming pool. Working alone, A, B and C require 10, 20 and 15 hours respectively. Find the total time required to fill the pool.
Answer: B
Let the capacity of the pool be LCM (10, 20, 15) = 60 units.
=> Efficiency of pipe A = 60 / 10 = 6 units / hour
=> Efficiency of pipe B = 60 / 20 = 3 units / hour
=> Efficiency of pipe C = 60 / 15 = 4 units / hour
=> Efficiency of pipe A and pipe C working together = 10 units / hour
=> Efficiency of pipe B and pipe C working together = 7 units / hour
=> Pool filled in first hour = 10 units
=> Pool filled in second hour = 7 units
=> Pool filled in 2 hours = 10 + 7 = 17 units
We will have 3 cycles of 2 hours each such that A and C, and, B and C work alternatively.
=> Pool filled in 6 hours = 17 x 3 = 51 units
=> Pool empty = 60 – 51 = 9 units
Now, these 9 units would be filled by A and C working together with the efficiency of 10 units / hour.
=> Time required to fill these 9 units = 9/10 hour = 0.9 hours = 54 minutes
Therefore, total time required to fill the pool = 6 hours 54 minutes
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Two pipes A and B can fill a tank in 6 hours and 4 hours respectively. If they are opened on alternate hours and if pipe A is opened first, in how many hours, the tank shall be full ?
Answer: B
(A+B)'s 2 hour's work when opened =
Now, its A turn in 5th hour
1/6 work will be done by A in 1 hour
Total time = 4 + 1 = 5 hours
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Two taps can separately fill a cistern 10 minutes and 15 minutes respectively and when the waste pipe is open, they can together fill it in 18 minutes. The waste pipe can empty the full cistern in?
Answer: D
\(1/10 + 1/15 - 1/x = 1/18\)
\(x = 9\)
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