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.
Amaterasu said:
5 years ago
Consider 1st, 2nd and 3rd pipe as a,b,c.
Given 1/a+1/b=1/c or a+b/ab=1/c because the time taken to fill by a and b is same is c
b=a-5 can be written as a=b+5.
b=c+4.
1st put value of a in a+b/ab=1/c then u get 2b+5/(b+5)b = 1/c
Then put the value of b you will get c=6 so b will 10 and a will be 15.
And the time taken by a is 15hr.
Given 1/a+1/b=1/c or a+b/ab=1/c because the time taken to fill by a and b is same is c
b=a-5 can be written as a=b+5.
b=c+4.
1st put value of a in a+b/ab=1/c then u get 2b+5/(b+5)b = 1/c
Then put the value of b you will get c=6 so b will 10 and a will be 15.
And the time taken by a is 15hr.
(16)
Sarbajit rai said:
5 years ago
@Ghousia,
Here the question says to find the time and thus it is logical that lesser the time it takes faster will be the work in filling the tank. For instance, car A is moving faster than car B by 10 kmph means car A is taking less time to cover the same as that of car B. That is the reason why 1/x+1/ (x-5) =1/(x-9).
Here the question says to find the time and thus it is logical that lesser the time it takes faster will be the work in filling the tank. For instance, car A is moving faster than car B by 10 kmph means car A is taking less time to cover the same as that of car B. That is the reason why 1/x+1/ (x-5) =1/(x-9).
(3)
SHUBHADIP DAS said:
5 years ago
In how much time 2nd and 3rd pipe together fo the work? Please explain the answer.
(2)
Anonymous said:
4 years ago
Thanks @Sai Krishna.
Hitesh said:
3 years ago
Here we got 2 answers.
3 and 15 but for 3 we will get y= -2 from y+5 =x,
So, x = 15.
3 and 15 but for 3 we will get y= -2 from y+5 =x,
So, x = 15.
(4)
Yogi said:
3 years ago
Thanks a lot for your explanation @Nita.
(4)
DEVINDER SINGH said:
2 years ago
Why equating work of a+b = work of c.
till the time we used the method
a = x-5
b = x
c =x-4.
Acc to the question.
(x-5) + x = x-4 on solving;
a = 4.
b = 9.
c = 13 which seems feasible acc conditions and also we used earlier questions.
till the time we used the method
a = x-5
b = x
c =x-4.
Acc to the question.
(x-5) + x = x-4 on solving;
a = 4.
b = 9.
c = 13 which seems feasible acc conditions and also we used earlier questions.
(10)
Rekha said:
1 year ago
Why it is 1 as a numerator? Please explain to me.
(4)
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