Two pipes A and B can fill a cistern in 24 and 36 minutes respectively. Both pipes are opened together, after how many minutes should B be turned off, so that the cistern be fill in 16 minutes?

Question: Two pipes A and B can fill a cistern in 24 and 36 minutes respectively. Both pipes are opened together, after how many minutes should B be turned off, so that the cistern be fill in 16 minutes?

Solution:
A can fill the cistern in 24 minutes
So in 1 min A can fill the cistern = 1/24 part
In 16 min, A can fill the cistern = 16/24 part
= 2/3 part

Remaining part = 1 - 2/3 = 1/3 rd

As B can fill full cistern in 36 minutes
So it will fill 1/3 rd part in = (1/3 × 36) minutes.
= 12 minutes.