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 4 of 9.
Leela said:
8 years ago
Thanks @Deepak.
Arjun said:
8 years ago
Nice work @Kasi Srinivas.
Khagendra said:
8 years ago
@Kasi Srinivas.
Nice explanation, anyone can easily understand this, Thanks.
Nice explanation, anyone can easily understand this, Thanks.
Tapz patel said:
8 years ago
A*(A'work)+B*(B'work)=1,
It means 30(A)+x(B)=1,
Then, x=9.
It means 30(A)+x(B)=1,
Then, x=9.
Deepak said:
8 years ago
Best solution:
Parts filled by A in 1 min = 2/75
Parts filled by B in 1 min = 1/45
Now;
In 30 min tank is full so,
Parts filled by A in 30 min = 30*2/75 =60/75
Parts filled by B in X min = X/45
So, 60/75 + X/45 = 1
Therefore ,X = 9 min.
Parts filled by A in 1 min = 2/75
Parts filled by B in 1 min = 1/45
Now;
In 30 min tank is full so,
Parts filled by A in 30 min = 30*2/75 =60/75
Parts filled by B in X min = X/45
So, 60/75 + X/45 = 1
Therefore ,X = 9 min.
Abhijeet Pol said:
8 years ago
Much simple way is the LCM method.
LCM of (75/2 and 45) = 225, assume this is total unit of work.
Thus, efficiency of A = [(225)/(75/2)] = 6 units/min and B = 225/45 = 5 units/min.
Since A works for 30 mins, he will finish = 6 x 30 = 180 units.
Remaining = 225 - 180 = 45 units to be completed by B in = (45/5) = 9 mins.
LCM of (75/2 and 45) = 225, assume this is total unit of work.
Thus, efficiency of A = [(225)/(75/2)] = 6 units/min and B = 225/45 = 5 units/min.
Since A works for 30 mins, he will finish = 6 x 30 = 180 units.
Remaining = 225 - 180 = 45 units to be completed by B in = (45/5) = 9 mins.
(1)
Manikant said:
8 years ago
2/75 + 1/45 = 8/225.
How it can be 11/225?
How it can be 11/225?
Sandhiya said:
8 years ago
Can anyone explain how 2/75 comes? please.
Madhubala said:
8 years ago
For 1min it takes( 2/75).
For 30 min (1/2 hour) it takes 2/75*30=4/5 part.
So remaining only 1 part out of 5 which is going to fill by B.
So (1/5*45) = 9 min.
For 30 min (1/2 hour) it takes 2/75*30=4/5 part.
So remaining only 1 part out of 5 which is going to fill by B.
So (1/5*45) = 9 min.
Kunal Aryan said:
9 years ago
For this type of question use Short Trick :
[Y*(1 - t / x)]
Here X= 75/2 ; Y=45 and t= 30mint. (ie. half an hour).
Soln: 45*(1 - 30 * 2 / 75) = 9 mints. answer.
[Y*(1 - t / x)]
Here X= 75/2 ; Y=45 and t= 30mint. (ie. half an hour).
Soln: 45*(1 - 30 * 2 / 75) = 9 mints. answer.
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