Tuesday, February 23, 2010

The Bridge


Four men want to cross a bridge. They all begin on the same side. It is night, and they have only one flashlight with them. At most two men can cross the bridge at a time, and any party who crosses, either one or two people, must have the flashlight with them.

The flashlight must be walked back and forth: it cannot be thrown, etc. Each man walks at a different speed. A pair must walk together at the speed of the slower man. Man 1 needs 1 minute to cross the bridge, man 2 needs 2 minutes, man 3 needs 5 minutes, and man 4 needs 10 minutes. For example, if man 1 and man 3 walk across together, they need 5 minutes.
 
What is the minimum time taken by the four men to cross the bridge and how?
Posted by at
Labels:

1 comment:

  1. ArindamMarch 4, 2010 at 2:20 AM

    Solution to the puzzle:
    First man 1 and man 2 walk across the bridge. This takes 2 minutes.
    After this, man 1 walks back with the flashlight. This takes 1 minute.
    Then man 3 and man 4 walk across the bridge. This takes 10 minutes.
    After this, man 2 walks back with the flashlight. This takes 2 minutes.
    Then man 1 and man 2 walk across the bridge. This takes 2 minutes as before.
    Total: 2+1+10+2+2=17 minutes.

    ReplyDelete

Subscribe to: Post Comments (Atom)