Two pipes P and Q can fill a cistern in 12 and 14 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? Choose the correct choice from the following choices
A) 1/8
B) 1/4
C) 1/2
D) 1/4
E) 1/4
3/12 + x/14   = 1   x= 10 1/2   Answer: 1/2
<result>C</result>
Two pipes P and Q can fill a cistern in 12 and 14 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?