Two pipes P and Q can fill a cistern in 12 and 15 minutes respectively. Both are opened together, but at the end of 3 minutes the first is turned off. How much longer will the cistern take to fill? Choose the correct choice from the following answers.
A) 11 1/8
B) 11 1/4
C) 11 2/4
D) 12 1/4
E) 17 1/4
3/12 + x/15   = 1   x= 11 1/4   Answer: 11 1/4
<result>B</result>
Two pipes P and Q can fill a cistern in 12 and 15 minutes respectively. Both are opened together, but at the end of 3 minutes the first is turned off. How much longer will the cistern take to fill?