Two pipes P and Q can fill a cistern in 12 and 18 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.
A) 13 1/2 min	B) 11 1/4 min	C) 11 2/4 min	D) 11 1/5 min	E) 11 7/4 min
3/12 + x/18 = 1   x= 13 1/2   13 1/2 minnswer: 13 1/2 min
<result>A</result>
Two pipes P and Q can fill a cistern in 12 and 18 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?