In the puzzle Four people on a Bridge we met four people who needed to cross a bridge at night. In this puzzle, there are five people who must cross two sequential bridges at night. As in the original puzzle, there are some hindrances:

The bridges can only support two people crossing at a time.

Each person has a different speed in which they can cross: 10 minutes, 7 minutes, 5 minutes, 2 minutes, and 1 minute.

They have only two flashlights to share among them.

What is the shortest amount of time it will take for all five people to cross both bridges?

keep in mind that there are two bridges...so lets use them both. i use the time it takes them to cross to represent them.

Bridge 1- 10 and 7 cross w/flashlight                   10 min 

Bridge 2- 5 and 1 cross  w/flashlight                   5 min

Bridge 2- 1 goes back w/ flashlight                     1 min

Bridge 2- 1 and 2 cross w/ flashlight                    2 min

now, if you add up the numbers for bridge 2, its 8 minutes. so 5,1, and 2 can all cross bridge 2 before  10 and 7 even get across bridge 1. so the minimum time it would take is 10 min.

 

Posted by Lacey on 2005-07-05 19:19:29