Addition theorem: P(A∪B) = P(A) + P(B) - P(A∩B). For mutually exclusive: P(A∪B) = P(A) + P(B). Complement rule: P(A') = 1 - P(A). Conditional probability: P(A|B) = P(A∩B)/P(B). Independent events: P(A∩B) = P(A)×P(B); P(A|B) = P(A). Multiplication rule: P(A∩B) = P(A)×P(B|A). Example: Cards. P(red or ace) = 26/52 + 4/52 - 2/52 = 28/52 = 7/13. Two draws without replacement: P(both red) = 26/52 × 25/51. Exam tip: Distinguish mutually exclusive from independent. Use Venn diagrams. Practice: Complex event combinations.