Four travelers need to cross a river at night. The ferry can carry at most two people, and they must use a lantern to see. The lantern must always be on the ferry, and it takes passengers 1, 3, 6, and 8 minutes to cross. When two cross together, they take the slower person's time. What is the fastest way to get everyone across?

Question

Accepted Answer

Send the 1- and 3-minute travelers across first (3 minutes), then send the 1-minute traveler back (1 minute). Next, send the 6- and 8-minute travelers across (8 minutes), then bring the 3-minute traveler back (3 minutes). Finally, send the 1- and 3-minute travelers across again (3 minutes). Total time: 18 minutes.

Midnight Ferry

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