Four people need to cross a bridge at night. They have one flashlight for the four of them, but the bridge is only wide enough for two to cross at a time. Because it's so dark, anyone crissing the bridge must do so with the flashlight.

Person A can walk across in 1 minute. Person B takes 2 minutes; person C -- 5 minutes, and finally person D needs a full 10 minutes to cross. Naturally, if two people are crossing the bridge, they move with the speed of the slower person.

What is the shortest amount of time it will take for all four to get to the other side?

I think that the shortest time it should take is 10 min-

If d holds the flashlight and d&c cross at the same time (d-c=5min) so after c has gone across d will still have 5 min so when c gets off then b can get on which will only take 2 min (5-2=3min) a will still have 3 min left when b gets off which will mean that a can cross and once a has crossed d will still have 2 min (3-1=2min) so therefore if d holds the flashlight each person will have light from d holding the light and it will take 10 min (the 10min it takes for d to get across) for them all to get across and there will still only be 2 people one the bridge at a time

I hope you look at this and think about it maybe

Posted by Awdreye on 2005-06-28 08:07:19