How can all four men cross the bridge in 17 minutes? Four men want to cross a bridge. They all begin on the same side. It is night and they have only one flashlight with them. At most two men can cross the bridge at a time and any party who crosses, either one or two people, must have the flashlight with them. The flashlight must be walked back and forth: it cannot be thrown, etc. Each man walks at a different speed. A pair must walk together at the speed of the slower man. Man 1 needs 1 minute to cross the bridge, man 2 needs 2 minutes, man 3 needs 5 minutes, and man 4 needs 10 minutes. For example, if man 1 and man 3 walk across together, they need 5 minutes.



Man 1 (1min) and Man 2 (2min) walk across first bringing the total to 2 minutes. Then Man 1 (1) walks the flashlight back, totaling 3 minutes. Man 3 (5)and Man 4 (10) walk across, totaling 13 minutes. Man 2 (2) walks the light back, totaling 15 minutes. Man 2 (2) and Man 1 (1) walk across, totaling the answer, 17 minutes.
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