Question:
Three taps A, B and C can fill a tank in 12, 15 and 20 hours respectively. If A is open all the time and B and C are open for one hour each alternately, the tank will be full in:
[A].6 hours
7 hours
Three taps A, B and C can fill a tank in 12, 15 and 20 hours respectively. If A is open all the time and B and C are open for one hour each alternately, the tank will be full in:
[A].
[B].
| 6 | 2 | hours |
| 3 |
[C].
[D].
| 7 | 1 | hours |
| 2 |
Answer: Option C
Explanation:
| (A + B)’s 1 hour’s work = | 1 | + | 1 | = | 9 | = | 3 | . | ||
| 12 | 15 | 60 | 20 |
| (A + C)’s hour’s work = | 1 | + | 1 | = | 8 | = | 2 | . | ||
| 12 | 20 | 60 | 15 |
| Part filled in 2 hrs = | 3 | + | 2 | = | 17 | . | ||
| 20 | 15 | 60 |
| Part filled in 6 hrs = | 3 x | 17 | = | 17 | . | ||
| 60 | 20 |
| Remaining part = | 1 – | 17 | = | 3 | . | ||
| 20 | 20 |
| Now, it is the turn of A and B and | 3 | part is filled by A and B in 1 hour. |
| 20 |
Total time taken to fill the tank = (6 + 1) hrs = 7 hrs.