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 5 of 7.
Lakshmichandra said:
10 years ago
Here why we can not consider x+5? I did not understand this problem can any please explain?
Deepak Pareek said:
1 decade ago
Solve through options. It will be easier.
Vicky said:
1 decade ago
Can you explain that 1/x-9 how come to right hand side positive.
Its positive on left side so it may be come to the right side than the equation -1/x-9.
Please any body explain.
Its positive on left side so it may be come to the right side than the equation -1/x-9.
Please any body explain.
Lakshmi said:
1 decade ago
Why neglecting 3 in the answer please can any one say?
Chandni said:
1 decade ago
I solved it by taking 2nd pipe's speed as x.
Then 1st pipe speed would be x-5 and 3rd pipe = x+4.
If we resolve now, we get y = -10 and y = 2.
So, I was finding answer according to 2.
Then 1st pipe speed would be x-5 and 3rd pipe = x+4.
If we resolve now, we get y = -10 and y = 2.
So, I was finding answer according to 2.
(1)
Sameeera said:
1 decade ago
Why can't we solve it in this way:
Let c=3rd pipe, b=2nd pipe, a=1st pipe.
Let us fix c's time = x.
c=x ; a=x+9; b=x+4.
(a+b)'s time =c's time.
1/(x+9) + 1/(x+4) = 1/x.
By solving we get x=6.
Now a=9+6=15.
Ok I think you have understood.
Let c=3rd pipe, b=2nd pipe, a=1st pipe.
Let us fix c's time = x.
c=x ; a=x+9; b=x+4.
(a+b)'s time =c's time.
1/(x+9) + 1/(x+4) = 1/x.
By solving we get x=6.
Now a=9+6=15.
Ok I think you have understood.
Inu said:
1 decade ago
Time cannot be negative. Thats why 3 is neglected.
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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