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.
Brryne said:
9 years ago
Dear Friends. The solution according to me is correct.
The reason as to why X = 3 is neglected is because there is no negative time.
For example: 3 hrs. If you substitute X with 3, then,
1/(x-5) will be 1/(3-5).
Which are 1/-2 hours (negative thirty minutes: never in real life!)
The reason as to why X = 3 is neglected is because there is no negative time.
For example: 3 hrs. If you substitute X with 3, then,
1/(x-5) will be 1/(3-5).
Which are 1/-2 hours (negative thirty minutes: never in real life!)
Minion said:
9 years ago
@Sameeera.
Your solution seems to be apt to this problem. Thank you.
Your solution seems to be apt to this problem. Thank you.
Robot said:
9 years ago
If you assume the value corresponding to the second pipe to be x,
The other two factors would be x + 5, x - 4 with respect to the 1st and the 3rd pipe.
Here,
1/ (x) + 1/ (x + 5) = 1/ (x - 4).
In this case, the answer turns out to be 10.
Help me.
The other two factors would be x + 5, x - 4 with respect to the 1st and the 3rd pipe.
Here,
1/ (x) + 1/ (x + 5) = 1/ (x - 4).
In this case, the answer turns out to be 10.
Help me.
Lalitha said:
9 years ago
Why you neglect 3?
Debasish said:
9 years ago
Is there any shortcut method for solving it?
Virajgouda said:
9 years ago
Why do you neglect 3? What is the reason?
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.
Bhagyasree said:
8 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.
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