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 choices:  A) 9 1/4 min  B) 11 1/4 min  C) 7 1/4 min  D) 8 1/2 min  E) 9 1/2 min
3/12 + x/15 = 1   x= 11 1/4   ANSWER:11 1/4 min
<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?