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 8 of 9.
Kouser said:
9 years ago
Good explanation @Kasi Srinivas.
Ashok said:
9 years ago
Go from the option.
Choose option 9 minutes and use it in B 1 minute work = 1/45 and find it for 9 minutes it's 1/5 then go for remaining works it is 1-1/5 = 4/5. This remaining work will be done by A then.
4/5 work in 75/2 minutes 4/5 * 75/2 = 30 that is the given minutes taken to fill the tank.
Choose option 9 minutes and use it in B 1 minute work = 1/45 and find it for 9 minutes it's 1/5 then go for remaining works it is 1-1/5 = 4/5. This remaining work will be done by A then.
4/5 work in 75/2 minutes 4/5 * 75/2 = 30 that is the given minutes taken to fill the tank.
Azharudhin said:
9 years ago
Hi @Meraj Husain, please explain how 60 came?
Your explanation is nice, please explain clearly once again. Thank you for your comments.
Your explanation is nice, please explain clearly once again. Thank you for your comments.
Azharudhin said:
9 years ago
Nice explanation @Mahesh Patil. Thank you.
Amit said:
10 years ago
Simply put A can fill in 75/2 minutes.
Therefore in 1 min it fills 2/75 part.
Therefore in 30 min it will fill 2*30/75 = 4/5th part.
Now after 30 min amount remaining to be filled will be 1-4/5 = 1/5.
(In above subtraction 1 means whole cistern), so now B has to fill 1/5 i.e. remaining part. Question is how many minute does B takes to fill 1/5 part of the cistern.
We know from question that B takes 45 min to fill the cistern.
Therefore in 1 minute fill 1/45th part.
Therefore x *1/45 = 1/5 (where x= minute it actually takes to fill the cistern).
Solving X = 9 minutes.
Therefore in 1 min it fills 2/75 part.
Therefore in 30 min it will fill 2*30/75 = 4/5th part.
Now after 30 min amount remaining to be filled will be 1-4/5 = 1/5.
(In above subtraction 1 means whole cistern), so now B has to fill 1/5 i.e. remaining part. Question is how many minute does B takes to fill 1/5 part of the cistern.
We know from question that B takes 45 min to fill the cistern.
Therefore in 1 minute fill 1/45th part.
Therefore x *1/45 = 1/5 (where x= minute it actually takes to fill the cistern).
Solving X = 9 minutes.
Hardik said:
10 years ago
Both together can do a work in 225/11 minute.
Now pipe A can do a work in 75/2 minute. He alone did work for 30 minutes in last.
30*2/75=4/5.
Now 1/5 had been filled by a and b together. 1 cistern in 225/11 minutes then 1/5 in how many minutes ?
Now pipe A can do a work in 75/2 minute. He alone did work for 30 minutes in last.
30*2/75=4/5.
Now 1/5 had been filled by a and b together. 1 cistern in 225/11 minutes then 1/5 in how many minutes ?
Shekhar ssc said:
10 years ago
Let A one min work = 1/37.5 = 2/75.
Let B one min work = 1/45.
Let B turn off after x min.
And so tank filled in 30 min.
So Tank full = Part filled by A and B + Part filled by only A.
1 = (A+B)x+(30-x)A.
1 = 11x/225+(30-x)2/75.
That's way x = 9.
Let B one min work = 1/45.
Let B turn off after x min.
And so tank filled in 30 min.
So Tank full = Part filled by A and B + Part filled by only A.
1 = (A+B)x+(30-x)A.
1 = 11x/225+(30-x)2/75.
That's way x = 9.
Bryan said:
10 years ago
I'm here with an easy solution.
In 1 min A fill 2/75 of tank. In 30 min A fill 30*2/75 = 4/5 of tank since A is turned on for 30 min while B is shut after few mins that we have to find:
Now tank which B will fill in x min = 1-4/5 = 1/5.
Now work/work in 1 min = Total no. of min (x).
(1/5)/(1/45) = x.
So x = 9 min.
In 1 min A fill 2/75 of tank. In 30 min A fill 30*2/75 = 4/5 of tank since A is turned on for 30 min while B is shut after few mins that we have to find:
Now tank which B will fill in x min = 1-4/5 = 1/5.
Now work/work in 1 min = Total no. of min (x).
(1/5)/(1/45) = x.
So x = 9 min.
Ashu said:
10 years ago
Why x is multiplied by total work?
Swetha said:
1 decade ago
How Part filled by (A + B) in x min + Part filled by A in (30 -x) min = 1?
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