Did I Get This – Conditional Probability
Consider the piercing example, where the following two-way table is given,
Recall also that M represents the event of being a male (“not M” represents being a female), and E represents the event of having one or both ears pierced.
http://phhp-faculty-cantrell.sites.medinfo.ufl.edu/files/2012/12/DIG_07004_111.swf
This document is linked from Conditional Probability and Independence.