Aptitude - Pipes and Cistern - Discussion
Discussion Forum : Pipes and Cistern - General Questions (Q.No. 10)
10.
Two pipes A and B can fill a tank in 15 minutes and 20 minutes respectively. Both the pipes are opened together but after 4 minutes, pipe A is turned off. What is the total time required to fill the tank?
Answer: Option
Explanation:
| Part filled in 4 minutes = 4 |  |
1 | + | 1 |  |
= | 7 | . |
| 15 | 20 | 15 |
| Remaining part = | |
1 - | 7 | |
= | 8 | . |
| 15 | 15 |
| Part filled by B in 1 minute = | 1 |
| 20 |
 |
1 | : | 8 | :: 1 : x |
| 20 | 15 |
| x = | |
8 | x 1 x 20 | |
= 10 | 2 | min = 10 min. 40 sec. |
| 15 | 3 |
The tank will be full in (4 min. + 10 min. + 40 sec.) = 14 min. 40 sec.
Discussion:
37 comments Page 3 of 4.
Preeti said:
1 decade ago
Another method could be : (1/15 + 1/20)*4 + (1/20)*x-4 = 1
7/15 + (X-4)/20 = 1
Hence x=44/3.
= 14(2/3) mins
= 14 min 40 seconds ( 2/3 x 60 = 40 seconds)
Here 7/15 is the part filled by (A + B) in 4 mins.
and (x-4) is the total time taken to fill the tank by B alone.
Here 1 means show full tank.
7/15 + (X-4)/20 = 1
Hence x=44/3.
= 14(2/3) mins
= 14 min 40 seconds ( 2/3 x 60 = 40 seconds)
Here 7/15 is the part filled by (A + B) in 4 mins.
and (x-4) is the total time taken to fill the tank by B alone.
Here 1 means show full tank.
D Priya said:
8 years ago
@Leela.
To fulfil the condition they equate to 1. A part of work + remaining part of work = 1. To be precise, you and your friend are doing a work by sharing. You completed half the work and your friend completed half the remaining work. Ie 1/2 + 1/2 = 1.
This logic is being used in this kind of problems.
To fulfil the condition they equate to 1. A part of work + remaining part of work = 1. To be precise, you and your friend are doing a work by sharing. You completed half the work and your friend completed half the remaining work. Ie 1/2 + 1/2 = 1.
This logic is being used in this kind of problems.
Leela said:
8 years ago
Can anyone tell me why do we equate to one?
Manisha said:
8 years ago
It is clear now Thank you, @Ashim.
Pavi said:
1 decade ago
Thank you sundar.
Venky said:
8 years ago
Can anyone explain it in easy method?
Ashim said:
9 years ago
LCM of 15 & 20 is 60.
(4 + 3) * 4 = 28.
60 - 28 = 32.
4 + 32/3 =14min = 40sec.
(4 + 3) * 4 = 28.
60 - 28 = 32.
4 + 32/3 =14min = 40sec.
Sandy said:
9 years ago
Super solution @Kalpna.
Neha said:
9 years ago
How to change the fraction value into minutes?
Ramees said:
10 years ago
Easy to convert 44/3 into 14(2/3).
Divide 44 into 3 we get remainder 2(i.e 14*3 = 42).
Then we can write 14 (remainder/3) that is 14(2/3).
Divide 44 into 3 we get remainder 2(i.e 14*3 = 42).
Then we can write 14 (remainder/3) that is 14(2/3).
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