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:
69 comments Page 7 of 7.
Lalitha said:
1 decade ago
Why you neglect 3?
Debasish said:
1 decade ago
Is there any shortcut method for solving it?
Virajgouda said:
1 decade ago
Why do you neglect 3? What is the reason?
Prawesh Pradhan said:
10 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.
Bhagyasree said:
9 years ago
Suppose A takes x hours then B takes x-5 hours.
Ex: It means that A completed in 10 hours where B Completed only in 5 hours
Now C take y hours where B Completes in y+4 hours(slower),
So x-5 =y+4..............y=x-9,
Here capability of A+B = C,
1/x+1/x-5 = 1/y,
Now, You can easily solve this eq 1/x+1/x-5 = 1/x-9.
Ex: It means that A completed in 10 hours where B Completed only in 5 hours
Now C take y hours where B Completes in y+4 hours(slower),
So x-5 =y+4..............y=x-9,
Here capability of A+B = C,
1/x+1/x-5 = 1/y,
Now, You can easily solve this eq 1/x+1/x-5 = 1/x-9.
Reshma said:
9 years ago
Nice explanation @Tanu.
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.
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.
SABYASACHI said:
1 decade ago
How it became (x-5) and (x-9) ?
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