Bridge and torch puzzle: how to solve it

In the famous "bridge and torch" puzzle, a group of four people must cross a bridge at night using only one torch. Each person varies in their crossing speed, with Alice taking 1 minute, Ben taking 2 minutes, Cindy taking 5 minutes, and Don taking 8 minutes. The challenge is to find a strategy that allows everyone to cross the bridge within 15 minutes. This was reported by SSPDaily.

To solve this puzzle, the following steps can be taken:

1. Alice and Ben cross the bridge together, which takes 2 minutes.

2. Alice, being the fastest, returns to the starting side with the torch in 1 minute. Alice has now spent a total of 3 minutes, and Ben is on the other side.

3. Next, Cindy and Don, who are the slowest, cross the bridge together, taking 8 minutes. Cindy and Don have now spent a total of 8 minutes, while Alice has crossed twice.

4. Ben, who is now on the other side, returns to the starting side in 2 minutes. Ben has now spent a total of 2 minutes, while Alice has crossed three times.

5. Finally, Alice and Ben cross the bridge together one last time, taking 2 minutes. Alice and Ben have now spent a total of 2 minutes, reaching a cumulative time of 15 minutes.

By following this strategy, all four people successfully cross the bridge within the given time frame of 15 minutes. Through a combination of efficient crossing pairs and strategic sequences, they managed to overcome the challenge of the limited torch, ensuring a safe and timely passage for everyone involved.

This solution demonstrates the importance of logical thinking and collaboration when faced with complex problems.