Two pipes A and B can fill a cistern in 12 and 15 minutes respectively. Both are opened together but after 2 minutes A is turned off. After how much more time will the cistern be filled?  Pick.
A) 8 1/7  B) 8 1/1  C) 8 1/4  D) 10 1/2  E) 8 3/7
2/12 + (2 + x)/15 = 1   x = 10 1/2   Answer: 10 1/2
<result>D</result>
Two pipes A and B can fill a cistern in 12 and 15 minutes respectively. Both are opened together but after 2 minutes A is turned off. After how much more time will the cistern be filled?