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 4 of 7.
Pradhyumna said:
8 years ago
Can't we pick the 'B' to be as x and do the same things since When I did I got four first just by generally calculating it?
Deepi said:
1 decade ago
@ venky
See the question they have given as second pipe 5 hours faster than the first and 4 hours slower than third.
Lets consider first pipe takes X hrs for ex. 10hrs
Second pipe takes 5 hours faster than first it means 5hrs (X-5)
Third pipe is faster than second by 4hrs. That is 1hour(10-9)=(X-9).
See the question they have given as second pipe 5 hours faster than the first and 4 hours slower than third.
Lets consider first pipe takes X hrs for ex. 10hrs
Second pipe takes 5 hours faster than first it means 5hrs (X-5)
Third pipe is faster than second by 4hrs. That is 1hour(10-9)=(X-9).
NAGARJUNA said:
7 years ago
Can anyone help me?
If suppose A and B are filling a tank started at same time.
A alone can fill it in 'a' minutes B alone can fill it in 'b' minutes.
So we are taking (1/a)+(1/b)=1 to find the time.
But when they are filling it simultaneously why are we taking same (1/x+1/x-5=1/x-9)?
I think after completion of a ,b is started it means we have to take a+b right? But not (1/a)+(1/b).
If suppose A and B are filling a tank started at same time.
A alone can fill it in 'a' minutes B alone can fill it in 'b' minutes.
So we are taking (1/a)+(1/b)=1 to find the time.
But when they are filling it simultaneously why are we taking same (1/x+1/x-5=1/x-9)?
I think after completion of a ,b is started it means we have to take a+b right? But not (1/a)+(1/b).
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.
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.
Anonymous said:
4 years ago
Thanks @Sai Krishna.
Reshma said:
9 years ago
Nice explanation @Tanu.
Venky said:
1 decade ago
4 hours slower than the third pipe = means how we took 1/X-9 and that also like this 1/X +1/X-5= 1/X-9
third pipe speed we dont know ...the how {x-9}
third pipe speed we dont know ...the how {x-9}
Sai Krishna A said:
1 decade ago
@ghousia faster means in less time. if for example A takes 20hours then B takes(20-5=15)hours not 20+5=25hours. got it
Ghousia said:
1 decade ago
Why is x-9 and x-5 taken as the pipe speed is represented faster then it should be x+9 and x+5? Please clarify my doubt.
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