Four men need to cross a bridge at night:
- No more than two can cross at a time
- They need a flashlight to cross, and they have only one
- They all start on the west side and all need to end up on the east side
- They take 10, 5, 2, and 1 minutes to cross, respectively
What's the most efficient way for them to cross?
And to add a note of suspense: a madman turns up after 18 minutes to kill anyone left on the west side or still on the bridge (i.e., 19 minutes is not the correct answer!).
Thanks go to Darren—this tricky one is from him.