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?

When two people cross the bridge, one must re-cross it with the flash light and travel back again with another person. Let's star with person A and person B. It takes them 2 minutes to cross. Person A goes back across in 1 minute and takes person C across the bridge in 5 minutes. Again, person A takes 1 minute to go and retrieve person D. It takes the two of them 10 minutes to cross. So, 2+1+5+1+10= 19 minutes

Posted by Amanda on 2002-10-08 10:03:43