🟢 Stats: The Three Probability Rules

Everything in probability comes from three rules:

Addition (OR): P(A or B) = P(A) + P(B) - P(A and B) If mutually exclusive: P(A or B) = P(A) + P(B)

Multiplication (AND): P(A and B) = P(A) × P(B|A) If independent: P(A and B) = P(A) × P(B)

Complement (NOT): P(not A) = 1 - P(A) Useful trick: "probability of at least one" = 1 - P(none)