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 7 of 7.
Sai said:
1 decade ago
Why we have taken 1/x, 1/x-5, 1/x-9. Please can any one say me the reason?
Praneeth said:
1 decade ago
We have considered the x-5 and x-9 as time taken by 2nd and 3rd pipes, but after substituting x=3 we will get -2hr and -7hr respectively for the 2nd and third pipes.
So, we cant have negative values for time practically.
So, we cant have negative values for time practically.
Sachin said:
1 decade ago
How can a pipe fill in both 3 and 9 hours. Hows it possible?
Only one answer must be true?
which one how to get?
Only one answer must be true?
which one how to get?
(1)
Manasa said:
1 decade ago
@pranesh kumar
In options "3" is not given...so we considered 15
both "3" and "15" are correct.
@karthikeyan
In the question they given
The first two pipes operating simultaneously fill the tank(1/x+1/X-5)... in the same time means ("=") during which the tank is filled by the third pipe alone(1/X-9)
how much water gets filled up by the first two pipes in 1 hour...the same amount of water gets filled up by the third pipe in 1 hour.
In options "3" is not given...so we considered 15
both "3" and "15" are correct.
@karthikeyan
In the question they given
The first two pipes operating simultaneously fill the tank(1/x+1/X-5)... in the same time means ("=") during which the tank is filled by the third pipe alone(1/X-9)
how much water gets filled up by the first two pipes in 1 hour...the same amount of water gets filled up by the third pipe in 1 hour.
Karthikeyan said:
1 decade ago
How got this equation 1/x+1/x-5=1/x-9 ?
(1)
Pranesh kumar said:
1 decade ago
Why you neglect x=3 for what reasons?
(1)
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)
Prasad said:
1 decade ago
How you have taken 9 hours?
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