|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:
|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|