Aptitude - Pipes and Cistern - Discussion
Discussion Forum : Pipes and Cistern - General Questions (Q.No. 5)
5.
A tank is filled by three pipes with uniform flow. The first two pipes operating simultaneously fill the tank in the same time during which the tank is filled by the third pipe alone. The second pipe fills the tank 5 hours faster than the first pipe and 4 hours slower than the third pipe. The time required by the first pipe is:
Answer: Option
Explanation:
Suppose, first pipe alone takes x hours to fill the tank .
Then, second and third pipes will take (x -5) and (x - 9) hours respectively to fill the tank.
 |
1 | + | 1 | = | 1 |
| x | (x - 5) | (x - 9) |
 |
x - 5 + x | = | 1 |
| x(x - 5) | (x - 9) |
(2x - 5)(x - 9) = x(x - 5)
x2 - 18x + 45 = 0
(x - 15)(x - 3) = 0
x = 15. [neglecting x = 3]
Discussion:
68 comments Page 4 of 7.
Thekingoftheworld said:
1 decade ago
The resolution here presented lies on the assumption that the volume is 1 cubic meter.
In fact, this problem would have infinite solution as no volume is specified in the question.
In fact, this problem would have infinite solution as no volume is specified in the question.
Pulkit said:
1 decade ago
Can anybody answer my question with correct explanation that why we have neglected x=3 and answered x=5. I know the explanation but I want to now that does anybody else knows it.
Nehal said:
8 years ago
By taking pipe b=x.
Then,
For others, it will be ...(x+5) for a.
And (x-4) for c.
Eq: 1/(x+5) +1/(x)=1/(x-4).
After solving ans comes as x=10.
Is it correct?
Then,
For others, it will be ...(x+5) for a.
And (x-4) for c.
Eq: 1/(x+5) +1/(x)=1/(x-4).
After solving ans comes as x=10.
Is it correct?
(2)
Tanu said:
1 decade ago
1st can fill tank in x hrs.
2nd can fill 5 hrs faster than 1st = x - 5.
3rd is 4 hr faster than 1st = (x - 5) -4 = x-9.
Hence,
1/x +1/(x-5) = 1/(x - 9).
2nd can fill 5 hrs faster than 1st = x - 5.
3rd is 4 hr faster than 1st = (x - 5) -4 = x-9.
Hence,
1/x +1/(x-5) = 1/(x - 9).
Venky said:
1 decade ago
4 hours slower than the third pipe = means how we took 1/X-9 and that also like this 1/X +1/X-5= 1/X-9
third pipe speed we dont know ...the how {x-9}
third pipe speed we dont know ...the how {x-9}
Vijay said:
1 decade ago
As 2nd one is 4 hrs slower than 3rd pipe, 3rd pipe should be 4 hrs faster than 2nd. So, 3rd pipe is 9 hrs faster than 1st one.
(2)
Pradhyumna said:
8 years ago
Can't we pick the 'B' to be as x and do the same things since When I did I got four first just by generally calculating it?
Ghousia said:
1 decade ago
Why is x-9 and x-5 taken as the pipe speed is represented faster then it should be x+9 and x+5? Please clarify my doubt.
Prawesh Pradhan said:
9 years ago
@Virajgouda, if take X as 3 the answer will be negative. And time can't be negative. X - 5 and x - 9 would be -2 and -6.
Sai Krishna A said:
1 decade ago
@ghousia faster means in less time. if for example A takes 20hours then B takes(20-5=15)hours not 20+5=25hours. got it
Post your comments here:
Quick links
Quantitative Aptitude
Verbal (English)
Reasoning
Programming
Interview
Placement Papers