Two pipes A and B can fill a cistern in 12 and 15 minutes respectively. Both are opened together but after 5 minutes A is turned off. After how much more time will the cistern be filled?	Choose the correct answer.
A) 8 1/7  B) 8 1/1  C) 3 3/4  D) 8 1/2  E) 8 3/7
5/12 + (5 + x)/15 = 1   x = 3 3/4   Answer: 3 3/4
<result>C</result>
Two pipes A and B can fill a cistern in 12 and 15 minutes respectively. Both are opened together but after 5 minutes A is turned off. After how much more time will the cistern be filled?