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 its 17 minutes. Here are the steps:

A + B goes across - 2 Minutes
A comes back - 1 minute.
C + D goes across - 10 minutes.
B comes back - 2 minutes.
A + B goes across - 2 minutes.

Obviously the flashlight just travels with the people who come back.

Posted by Lewis on 2003-06-07 08:04:18