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?
 
Solution: 
 http://www.math.utah.edu/~cherk/solutions/bridge/bridge.html