Bridge Crossing at Night

The Torch Challenge

Four people (A, B, C, D) need to cross a bridge at night.

Crossing times:

• A: 1 minute
• B: 2 minutes
• C: 5 minutes
• D: 10 minutes

Constraints:

• Only one torch available (someone must carry it back)
• Maximum two people on the bridge at once
• When two cross together, they move at the slower person's pace

Goal: Get everyone across in 17 minutes or less.

This is the famous bridge-and-torch puzzle!