Two pipes A and B can separately fill a tank in 20 minutes and 15 minutes respectively. Both the pipes are opened together but 4 minutes after the start the pipe A is turned off. How much time will it take to fill the tank? Choose the correct option:
A) 12min  B) 14min  C) 15min  D) 13min  E) 10min
4/20 + x/15 = 1   x = 12   12minNSWER:12min
<result>A</result>
Two pipes A and B can separately fill a tank in 20 minutes and 15 minutes respectively. Both the pipes are opened together but 4 minutes after the start the pipe A is turned off. How much time will it take to fill the tank?