A liquid container is usually filled up in 8 hours.
Due to a leak since the beginning, it took 2 hours more to fill the container.
The leak could empty the filled container in:
Let leak alone empty the tank in x hours.
Normal filling rate = 1/8 per hour
With leak → filled in 10 hours → net rate = 1/10
So,
1/8 − 1/x = 1/10
⇒ 1/x = 1/8 − 1/10 = (5 − 4)/40 = 1/40
Hence, leak alone can empty in 40 hours.
Two pipes A and B can fill a tank in 12 min and 16 min respectively. Both are opened together; after how much time should B be closed so that the tank gets filled in 9 min?