Probability & Combinatorics
Intermediate

Addition Rule

Probability that A or B occurs.

Formula

P(A∪B)=P(A)+P(B)−P(A∩B)P(A \cup B) = P(A) + P(B) - P(A \cap B)

Variables

A,BEvents
\capIntersection

Example

For mutually exclusive events the last term is 0

Did You Know?

Subtracting the intersection avoids double-counting.

probabilityunion