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 3 of 7.
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.
Inu said:
1 decade ago
Time cannot be negative. Thats why 3 is neglected.
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.
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)
Lakshmi said:
1 decade ago
Why neglecting 3 in the answer please can any one say?
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.
Deepak Pareek said:
1 decade ago
Solve through options. It will be easier.
Lakshmichandra said:
10 years ago
Here why we can not consider x+5? I did not understand this problem can any please explain?
Dipika Sinha Bhaduri said:
10 years ago
This question is a very easy one.
Let 2nd pipe's speed be x.
So 1st pipe's speed will be x+5.
And 3rd pipe's will be x-4 (as per the ques).
Now, it is given in the question that The first two pipes operating simultaneously fill the tank in the same time during which the tank is filled by the third pipe alone.
Hence 1/x + 1/x+5 = 1/x-4.
Solving this we get x = -2 and 10. Obviously x = 5 therefore speed of 1st pipe is 10+5 = 15.
Let 2nd pipe's speed be x.
So 1st pipe's speed will be x+5.
And 3rd pipe's will be x-4 (as per the ques).
Now, it is given in the question that The first two pipes operating simultaneously fill the tank in the same time during which the tank is filled by the third pipe alone.
Hence 1/x + 1/x+5 = 1/x-4.
Solving this we get x = -2 and 10. Obviously x = 5 therefore speed of 1st pipe is 10+5 = 15.
Vaisakh said:
10 years ago
Let first pipe alone takes x hours to fill the tank. Then if we take (x+5), it means 2nd pipe fills the tank 5 hours slower than the first pipe. So it's not possible. Just think about it.
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