Question 17
Four boys need to cross a dark tunnel but they only have a torch among them. A can cross the tunnel in 1 minute. B can cross the tunnel in 1.5 minutes. C can cross the tunnel in 2 minutes. D can cross the tunnel in 2.5 minutes. Given that they need a torch to cross at all time and that the tunnel can only allow passage of two children, find the least possible time needed for four boys to get across the tunnel.