Two pipes P and Q can fill a cistern in 11 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) 1/8 B) 1/4 C) 2/4 D) 10/11 E) 1/4
3/11 + x/15   = 1   x= 10 10/11   Answer: 10/11
<result>D</result>
Two pipes P and Q can fill a cistern in 11 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?