Aptitude - Pipes and Cistern - Discussion
Discussion Forum : Pipes and Cistern - General Questions (Q.No. 4)
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:
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:
Answer: Option
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.
 x |
 |
2 | + | 1 |  |
+ (30 - x). | 2 | = 1 |
| 75 | 45 | 75 |
 |
11x | + | (60 -2x) | = 1 |
| 225 | 75 |
11x + 180 - 6x = 225.
x = 9.
Discussion:
91 comments Page 10 of 10.
Prateeeeek said:
7 days ago
@All.
Here's my solution.
We know the 2/75 and 1/45 part (tank filled individually in a minute)
Now A will be left completely open for 30 minutes,
So 30*2/75 = 4/5,
So, 4/5th of the tank is filled by A, now 1/5th is left.
For B, 1/45 in 1min.
So in 1/5th in x mins.
Solving x, we get 45/5 i.e. 9.
Here's my solution.
We know the 2/75 and 1/45 part (tank filled individually in a minute)
Now A will be left completely open for 30 minutes,
So 30*2/75 = 4/5,
So, 4/5th of the tank is filled by A, now 1/5th is left.
For B, 1/45 in 1min.
So in 1/5th in x mins.
Solving x, we get 45/5 i.e. 9.
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