Four people need to cross a dark bridge with one flashlight. At most two can cross together, walking at the pace of the slower person. Person A takes 1 minute, B takes 2 minutes, C takes 7 minutes, and D takes 10 minutes. What is the minimum time in minutes for everyone to cross?
17 minutes
A and B cross first (2 min), A returns with the torch (1 min). C and D cross together (10 min), B returns with the torch (2 min). Finally, A and B cross together (2 min). Total time: 2 + 1 + 10 + 2 + 2 = 17 minutes.
About this riddle
Math riddles hide a calculation inside a short story. Pull out the numbers, work out what is being asked, and watch for a trick such as a unit change.
Difficulty: Hard. More like this: Math riddles with answers or try Target 24 for a different kind of puzzle.
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