Two pipes A and B can fill a cistern in 12 and 15 minutes respectively. Both are opened together but after 3 minutes A is turned off. After how much more time will the cistern be filled?	Choose the correct answer
A) 8 1/9	B) 8 1/0	C) 8 1/4	D) 8 1/3	E) 8 1/1
3/12 + (3 + x)/15 = 1   x = 8 1/4   Answer: 8 1/4
<result>C</result>
Two pipes A and B can fill a cistern in 12 and 15 minutes respectively. Both are opened together but after 3 minutes A is turned off. After how much more time will the cistern be filled?