Correct Option: A
On the basis of given details in question ,
| Part filled by A from 8 a.m to 11 a.m. = | 3 | = | 1 |
| 15 | 5 |
| Part filled by B from 9 a.m. to 11 a.m. = | 2 | = | 1 |
| 12 | 6 |
| Total Part filled till 11 a.m. = | 1 | + | 1 | = | 6 + 5 | = | 11 |
| 5 | 6 | 30 | 30 |
At 11 a.m. pipe C is opened to empty it.
| ∴ Part of tank emptied in 1 hour = | 1 | - | 1 | - | 1 |
| 4 | 15 | 12 |
| Part of tank emptied in 1 hour = | 15 - 4 - 5 | = | 1 |
| 60 | 10 |
| ∴ | 11 | part will be emptied in | 11 | × 10 = | 11 | hours or 3 | 2 |
| 30 | 30 | 3 | 3 |
i.e. 3 hours 40 minutes or at 11 : 40 a.m.
Therefore , the tank will be emptied at 11 : 40 a.m.
