Home>Probability of Event A OR Event B
Lesson by Mike McGarry
Magoosh Expert

Summary
Understanding the OR rule in probability is crucial for solving problems that involve calculating the likelihood of one event or another happening, especially in the context of the GRE exam.
• The simple OR rule applies when two events are mutually exclusive, meaning the probability of either event occurring is the sum of their individual probabilities.
• Mutually exclusive events are represented by non-overlapping circles, indicating no simultaneous occurrence, simplifying their combined probability to a straightforward addition.
• For non-mutually exclusive events, which can occur simultaneously, the general OR rule must be applied. This involves adding the probabilities of each event and then subtracting the probability of both events occurring together.
• The general OR rule, which accounts for the overlap (or simultaneous occurrence) of events, is universally applicable and corrects for the double counting of the overlap region.
• Visual aids, like Venn diagrams, are instrumental in understanding and applying these rules, especially in abstract or complex scenarios.
Chapters
00:00
Introduction to the OR Rule
00:15
The Simple OR Rule for Mutually Exclusive Events
01:20
Understanding Non-Mutually Exclusive Events
02:29
The General OR Rule for All Events