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 6 of 7.
SABYASACHI said:
1 decade ago
Is there any short tricks for this type of questions?
Tanu said:
1 decade ago
1st can fill tank in x hrs.
2nd can fill 5 hrs faster than 1st = x - 5.
3rd is 4 hr faster than 1st = (x - 5) -4 = x-9.
Hence,
1/x +1/(x-5) = 1/(x - 9).
2nd can fill 5 hrs faster than 1st = x - 5.
3rd is 4 hr faster than 1st = (x - 5) -4 = x-9.
Hence,
1/x +1/(x-5) = 1/(x - 9).
Rohit sharma said:
1 decade ago
Is it wrong if we suppose X time taken by the 2nd pipe and solve as per the problem i.e :
Time taken by 1st pipe : X+5.
Time taken by 2nd pipe : X.
And time taken by 3rd pipe : X-4.
Please explain me.
Time taken by 1st pipe : X+5.
Time taken by 2nd pipe : X.
And time taken by 3rd pipe : X-4.
Please explain me.
Chinna jgc said:
1 decade ago
2nd pipe is 5 hours faster than 1st.so 2nd pipe=5x
1st pipe automatically takes 1 hour to fill the tank.1st pipe=1x.
in question 2nd pipe is 4 hours slower than 3rd pipe.
i.e 5x+4x=9x
3rd pipe =9x
add all 3 pipes i.e 1x+5x+9x=15.
1st pipe automatically takes 1 hour to fill the tank.1st pipe=1x.
in question 2nd pipe is 4 hours slower than 3rd pipe.
i.e 5x+4x=9x
3rd pipe =9x
add all 3 pipes i.e 1x+5x+9x=15.
Rofiqul Hoque said:
1 decade ago
Let 1st pipe take time = x hours.
2nd pipe is 5 hours faster means its take 5 hours less than 1st pipe.
i.e., 2nd = (x-5) hours.
3rd pipe is 4 hours slower than the 2nd pipe.
i.e., 3rd +4 = (x-5).
=>3rd = (x-5) -4.
=>3rd = x-9.
Now,
1/x + 1/ (x-5) =1/ (x-9).
Dear friends now just solve it. Bye friends meet you again.
2nd pipe is 5 hours faster means its take 5 hours less than 1st pipe.
i.e., 2nd = (x-5) hours.
3rd pipe is 4 hours slower than the 2nd pipe.
i.e., 3rd +4 = (x-5).
=>3rd = (x-5) -4.
=>3rd = x-9.
Now,
1/x + 1/ (x-5) =1/ (x-9).
Dear friends now just solve it. Bye friends meet you again.
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).
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.
Kasi Srinivas said:
1 decade ago
@ sai :
first pipe alone takes x hours to fill the tank => in 1 hour 1/x part of the work is completed.
similar way we get 1/(x-5) and 1/(x-9) part of the work is completed in 1 hour.
it is the standard practice that we consider the work done in an hour.
If you understood the question properly, you can understand this :)
first pipe alone takes x hours to fill the tank => in 1 hour 1/x part of the work is completed.
similar way we get 1/(x-5) and 1/(x-9) part of the work is completed in 1 hour.
it is the standard practice that we consider the work done in an hour.
If you understood the question properly, you can understand this :)
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