❔ Four people need to cross a rickety bridge at night. They have one torch and different crossing times: 1, 2, 5, and 8 minutes. The bridge can only hold two people at a time, and they must walk at the speed of the slower person. What's the fastest way to get everyone across?
The key to solving this puzzle is minimizing the amount of time spent bringing the torch back across the bridge. The fastest person (Person 1) acts as the primary torch carrier, shuttling back and forth while ensuring the slowest two people cross together to avoid wasting time.
Optimal Solution: It takes 17 minutes to get all four people across the bridge.
Steps:
The two fastest cross first: Person 1 (1 minute) and Person 2 (2 minutes) cross together (2 minutes elapsed).
The fastest returns: Person 1 brings the torch back (3 minutes elapsed).
The two slowest cross: Person 5 (5 minutes) and Person 8 (8 minutes) cross together (11 minutes elapsed).
The second fastest returns: Person 2 brings the torch back (13 minutes elapsed).
The two fastest cross again: Person 1 and Person 2 cross together (15 minutes elapsed).
The fastest returns: Person 1 brings the torch back (16 minutes elapsed).
The two fastest cross a final time: Person 1 and Person 2 cross (17 minutes elapsed).