Four people (a, b, c, d) want to cross a bridge at night.  Person a takes 1 minute; peron b takes 2 minutes; person c takes 5 minutes, and person d takes 10 minutes.  They have only one torch and the bridge cannot be crossed without the torch.  There cannot be more than two people on the bridge at the same time; and, when two people cross the bridge together they move at the slower person's pace.  To win the game, a player must find a series of 5 crossings that gets all four people across the bridge in no more than 17 minutes.