Two pipes A and B can fill a tank in 10 and 20 minutes respectively.If both pipes are opened simultaneously,after how many minutes should pipe B be closed so that the tank is full in 8 minutes?
A. 3 min
B. 4 min
C. 2 min
D.5 min
Out of 8 crew members 3 particular members can sit only on the left side.Another 2 particular members can sit on the right side.Find the number of ways in which the crew can be arranged so that four men can sit on each side