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? Choices.
A) 11 1/8 min
B) 11 1/4 min
C) 11 8/4 min
D) 11 1/9 min
E) 11 3/4 min
3/12 + x/15   = 1   x= 11 1/4   Answer:11 1/4 min
<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?