Math
Probability rules.
Definition
The fundamental laws governing how probabilities combine. The addition rule finds the probability of either event occurring, while the multiplication rule finds the probability of both events occurring.
Examples
Real-world.
- 1 P(rolling a 2 or 4 on a die) = 1/6 + 1/6 = 2/6
- 2 P(two heads in a row) = 1/2 × 1/2 = 1/4
- 3 P(red or face card) = P(red) + P(face) - P(red and face) = 26/52 + 12/52 - 6/52
Key Fact
Addition: P(A or B) = P(A) + P(B) - P(A and B); Multiplication (independent): P(A and B) = P(A) × P(B)