Two pipes P and Q can fill a cistern in 12 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?
Choose the correct choice from the following answers.
A) 11 1/9  B) 11 1/4  C) 19 1/9  D) 11 1/2  E) 11 1/41
3/12 + x/15 = 1   x= 11 1/4   Answer: 11 1/4
<result>B</result>
Two pipes P and Q can fill a cistern in 12 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?