Learn by Doing: Independent Events
http://phhp-faculty-cantrell.sites.medinfo.ufl.edu/files/2012/12/LBD_07001_107.swf
http://phhp-faculty-cantrell.sites.medinfo.ufl.edu/files/2012/12/LBD_07002_107.swf
This document is linked from Conditional Probability and Independence.