Pipe A can fill a tank in 16 minutes and pipe B cam empty it in 24 minutes. If both the pipes are opened together after how many minutes should pipe B be closed, so that the tank is filled in 30 minutes?

A. 20
B. 24
C. 23
D. None of these

Explanation:

Let the pipe B be closed after x minutes.

30/16 – x/24 = 1 => x/24 = 30/16 – 1 = 14/16
=> x = 14/16 * 24 = 21.