Key Concepts: Probabilities of Mutually Exclusive Events

Mutually Exclusive Events

Two events are mutually exclusive (disjoint) if they cannot happen at the same time.

P(A or B) = P(A) + P(B)

Non-Mutually Exclusive Events

If events can happen at the same time:

P(A or B) = P(A) + P(B) − P(A and B)

Complement Rule

P(not A) = 1 − P(A)

Key Insight

Always check whether events overlap. If they do, subtract the overlap to avoid double counting.