Unions and Intersections

_Part Two

When two events cannot happen at the same time. They are called mutually exclusive or disjoint events.

Intersection

When two events occur at the same time, this is denoted as A ∩ B which is called the intersection of A and B.

Notation for the probability of both A and B happening.

P(A ∩ B)

Union

When either event A, event B, or both occur then we call this the union of A or B, which is denoted as A ∪ B.

Notation for the probability of either A, B, or both happening.

P(A ∪ B)

Rules

Addition Rule For any two events A and B

P(A ∪ B) = P(A) + P(B) - P(A ∩ B)

P(A and/or B) = P(A) + P(B) - P(A and B)