Four people need to cross a rickety rope bridge at night. They have only one flashlight, and the bridge can hold at most two people at a time. Their individual crossing times are 1, 2, 5, and 10 minutes. When two people cross together, they must walk at the pace of the slower person. What is the minimum total time required for all four people to cross to the other side?
17 minutes
1 and 2 cross first (2 min). 1 returns with flashlight (1 min). 5 and 10 cross together (10 min). 2 returns with flashlight (2 min). 1 and 2 cross together again (2 min). Total time = 2 + 1 + 10 + 2 + 2 = 17 minutes.
About this riddle
Logic riddles give you a few facts and ask what must be true. List what you know, cross out what cannot be, and see what is left.
Difficulty: Hard. More like this: Logic riddles with answers or try Einstein's Logic Grid for a different kind of puzzle.
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