Monday, June 13, 2011

Bridge crossing

  This problem was published in MAA on line: Crossing a Rickety Bridge at Night By Flashlight.
    A group of four people has to cross a bridge. It is dark, and they have to light the path with a flashlight. No more than two people can cross the bridge simultaneously, and the group has only one flashlight. It takes different time for the people in the group to cross the bridge:
      Annie crosses the bridge in 1 minute, 
      Bob crosses the bridge in 2 minutes, 
      Volodia Mitlin crosses the bridge in 5 minutes,
      Dorothy crosses the bridge in 10 minutes.
How can the group cross the bridge in 17 minutes?


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