Bridge Crossing Puzzle Solution

A group of four people has to cross a bridge. It is dark, and they have to light the path with a flashlight. No more than two people can cross the bridge simultaneously, and the group has only one flashlight. It takes different time for the people in the group to cross the bridge: Annie crosses the bridge in 1 minute Bob crosses the bridge in 2 minutes Carl crosses the bridge in 5 minutes Dorothy crosses the bridge in 10 minutes How can the group cross the bridge in 17 minutes?

Solution:

We shall list the solution in the first column, the time required for each task in the second column, and a running count of the time in the right column.
Action	Time Required	Running Time
1. Bob and Annie cross.	2 minutes	2 minutes
2. Bob comes back across alone.	2 minutes	4 minutes
3. Carl and Dorothy cross.	10 minutes	14 minutes
4. Annie comes back across.	1 minute	15 minutes
5. Annie and Bob head back across.	2 minute	17 minutes

Main || Personal | Puzzles | Bridge Crossing Solution