Solution to Riddle of the Week

Solution to Riddle of the Week: Crossing a Sketchy Rope Bridge

Difficulty level: Moderate

As always, if you haven't taken a crack at solving the riddle, you can see the question and a hint here. If it's giving you trouble, sleep on it, try Riddle of the Week #1, and come back to this problem with a fresh mind.

SOLUTION

The key to solving this riddle is sending the 5-minute person (the janitor) and the 10-minute person (the professor) across together. This way you get the two slowest people across in 10 minutes instead of 15, and that 5 minutes saved is worth the hassle of not being able to send the 1-minute person (you) back with the flashlight every time. You don't want the 5- or 10-minute person going back across though, so you need to leave one of the faster people on the far side waiting.

So, you send the 1-minute person and the 2-minute person (the lab assistant) across first. 2 minutes have elapsed. Then send the 1-minute person back with the flashlight. 3 minutes have elapsed. Then send the 5-minute person and the 10-minute person across together. 13 minutes have elapsed. Then send the 2-minute person back with the flashlight. 15 minutes have elapsed. Finally, send the 1-minute and 2-minute person across together, and everyone is across in 17 minutes. Congratulations, you escaped the zombies and lived to tell the tale.

Note: You can send the 2-minute person back across initially rather than the 1-minute person and still get everyone across in 17 minutes.