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 option:
A) 11 1/7
B) 11 1/4
C) 11 1/3
D) 11 1/2
E) 11 1/1
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?