Two pipes P and Q can fill a cistern in 10 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 choices.
A) 1/2  B) 1/4  C) 2/4  D) 1/4  E) 1/4
3/10 + x/15   = 1   x= 10 1/2   1/2nswer: 1/2
<result>A</result>
Two pipes P and Q can fill a cistern in 10 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?