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?	Pick one.
A) 11 1/5	B) 11 1/4	C) 11 1/9	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?