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 2 of 9.
Karansingh said:
6 years ago
There is a shorcut trick here.
Find lcm of 75 and 45.
Lcm is 225.
Divide by 75 and 45 to lcm.
Hereafter dividing lcm you will get 3 and 5.
Now given is that cistern will be filled in half hour means 30 min if b turned off.
They do 30/5 = 6.
Now add 3+6 = 9 (why to add this because we asked that if it is closed then we have to add that 3+6).
Find lcm of 75 and 45.
Lcm is 225.
Divide by 75 and 45 to lcm.
Hereafter dividing lcm you will get 3 and 5.
Now given is that cistern will be filled in half hour means 30 min if b turned off.
They do 30/5 = 6.
Now add 3+6 = 9 (why to add this because we asked that if it is closed then we have to add that 3+6).
(1)
Narula said:
7 years ago
The much simple way is the LCM method.
LCM of (75/2 and 45) = 225, assume this is a 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 a 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)
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)
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.
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.
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.
Hemant said:
9 years ago
In 1min=2/75 part of the cistern is filled by pipe A.
And In 1 min=1/45 part of the cistern is filled by pipe B.
Now,
Pipe A worked for 30 min and pipe B work for x min we suppose,
To fill complete cistern = 1 part.
2/75 * 30 + 1/45 * x = 1,
12/15 + x/45 = 1,
(36 + x)/45 = 1,
x = 9 min.
And In 1 min=1/45 part of the cistern is filled by pipe B.
Now,
Pipe A worked for 30 min and pipe B work for x min we suppose,
To fill complete cistern = 1 part.
2/75 * 30 + 1/45 * x = 1,
12/15 + x/45 = 1,
(36 + x)/45 = 1,
x = 9 min.
Hari said:
7 years ago
@Sarika.
Just take LCM of 37.5 and 45=450(total units).
You need 30mins to fully fill so(450/30)=15mins u have in total if Both worked non stop
now A works for a full period so 450/75 (convert 37.5 into the whole num as used for LCM)=6 mins.
So, B has worked 15-6=9mins.
Just take LCM of 37.5 and 45=450(total units).
You need 30mins to fully fill so(450/30)=15mins u have in total if Both worked non stop
now A works for a full period so 450/75 (convert 37.5 into the whole num as used for LCM)=6 mins.
So, B has worked 15-6=9mins.
Shruti said:
5 years ago
We get total amount to be filled by taking the LCM of (45,75/2) = 225litres.
Efficiency of A=225/(75/2)= 6litres/min
Efficiency of B=225/(45) = 5litres/min
So A in 30mins =30* 6 = 180litres
Remaining amount = 225 - 180 = 45L
Now B fills 5L in 1min,
45L it requires 9mins.
Efficiency of A=225/(75/2)= 6litres/min
Efficiency of B=225/(45) = 5litres/min
So A in 30mins =30* 6 = 180litres
Remaining amount = 225 - 180 = 45L
Now B fills 5L in 1min,
45L it requires 9mins.
(10)
Rohit said:
1 decade ago
Pipe A fills tank in 6 hours, pipe B in 8 hours. Both pipes opened simultaneously, then after how many hours should pipe B should be closed so that tank is filled in 4 hours.
I am getting a negative value and answer I am getting is 16/3 which is wrong. Please help.
I am getting a negative value and answer I am getting is 16/3 which is wrong. Please help.
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