Laws of Probability
The addition law states P(A ∪ B) = P(A) + P(B) - P(A ∩ B); for mutually exclusive events, P(A ∪ B) = P(A) + P(B). The multiplication law states P(A ∩ B) = P(A) × P(B | A); for independent events, P(A ∩ B) = P(A) × P(B).
Real World
Netflix engineers use the multiplication law to estimate the probability that two independent server failures occur simultaneously, since the events are independent and P(A ∩ B) = P(A) × P(B).
Exam Focus
State whether events are independent or mutually exclusive before selecting the correct law — examiners award method marks for this.
How well did you know this?