A SMALL PUZZLE

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,
Raju crosses the bridge in 5 minutes,
Dorothy crosses the bridge in 10 minutes.

          How can the group cross the bridge in 17 minutes?

a coins puzzle

There are 12 coins. One of them is false; it weights differently. It is not known, if the false coin is heavier or lighter than the right coins. How to find the false coin by three weighs on a simple scale?