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:
90 comments Page 5 of 9.
Vini said:
6 years ago
How will A become 2/75, can anyone explain?
Gunjan said:
6 years ago
Y(1-t/x).
X = 75/2.
Y =45.
T = 30.
This is the formula for this question.
X = 75/2.
Y =45.
T = 30.
This is the formula for this question.
Ruby said:
5 years ago
Another solution in term of common sense just for MCQ purpose:
The time that A takes to fill - 371/2= 37.5 min
The time that B takes more than A to fill - 45/37.5=1.2 times
After 30 min extra time would have been needed by A to fill - 7.5 minutes.
The time that B needs to compensate for - 7.5*1.2= 9 minutes.
The time that A takes to fill - 371/2= 37.5 min
The time that B takes more than A to fill - 45/37.5=1.2 times
After 30 min extra time would have been needed by A to fill - 7.5 minutes.
The time that B needs to compensate for - 7.5*1.2= 9 minutes.
Arun said:
5 years ago
Let 'B' be turned off after 'x' minutes.
Then:
Part filled by A and B in 1 minute:
[(2/75) + (1/x) ] = [1/30] minutes.
[(2x + 75) ] 30 = 75x.
x = 225/9 = 9 minutes(Ans).
Then:
Part filled by A and B in 1 minute:
[(2/75) + (1/x) ] = [1/30] minutes.
[(2x + 75) ] 30 = 75x.
x = 225/9 = 9 minutes(Ans).
Rohini said:
5 years ago
@Kasi.
Nice explanation.
Nice explanation.
Jothigonzi said:
5 years ago
@Abhijeet pol.
Nice and easiest explanation. Thanks.
Nice and easiest explanation. Thanks.
S.MEENAKSHI said:
1 decade ago
Excellent explanation KASI.
Shwetha cr said:
1 decade ago
1 indicates complete cistern.
Nins said:
1 decade ago
What is the meaning of "1" here?
Saurav said:
1 decade ago
Why x*(A+B)+A*(30-x) = 1.
It should be x*(A+B)+A*(30-x) = 1/2, because after 30 mins the tank should be half filled?
It should be x*(A+B)+A*(30-x) = 1/2, because after 30 mins the tank should be half filled?
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