Question

Question 1. With the method please.

Answer 1

Option (C) - 7 hours 12 minutes.

Per hour :

1. Six large pipes drain the reservoir at 1/12 per hour.

2. Six small pipes drain the reservoir at 1/18 per hour.

Together they can drain at 1/18 + 1/12 = 5/36 per hour.


The total time taken by both the pipes to drain = 36/5

                                                                                = 7.2 hours

                                                                                 = 7 hours 12 minutes.