Question:
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?
[A].10 min. 20 sec.
11 min. 45 sec.
12 min. 30 sec.
14 min. 40 sec.
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?
[A].
[B].
[C].
[D].
Answer: Option D
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.