Probability
Rules 0 ≤ P(A) ≤ 1 for any event A. P(S) = 1 Complement: P(A c ) = 1 – P(A) Addition: If A and B are disjoint events, P(A or B) = P(A) + P(B). Multiplication: If A and B are independent events, P(A and B) = P(A)P(B).
Reminder Disjoint – mutually exclusive (no outcomes in common, never occur simultaneously, one happens then the other. Independent – knowing one outcome doesn’t change the other outcome.
Joint Probability JOINT – (opposite of disjoint) mutually inclusive (some common outcomes, can occur simultaneously). The union is less than the sum of the individual probabilities. P(A or B) = P(A) + P(B) – P(A and B). P(A or B) = P(A) + P(B) – P(A and B).
Exercises 6.27, 6.30, 6.31, 6.33, , 6.46, 6.47, 6.52, 6.53
Conditional Probability Probability changes if we know that some other event has occurred. New Notation: P(A|B) read “Probability of A given the information about the probability of B”
Multiplication Rule The probability that both of two events A and B happens together P(A and B) = P(A)P(B|A) P(A and B) = P(A)P(B|A) Conditional is P(B|A) which is to say that B occurs given that A occurs.
Conditional Probability When P(A) > 0, the conditional probability of B given A is P(B|A) = P(A and B)/ P(A) Homework: 6.54 – 6.56
Extended Multiplication Rules Intersection – the event that all of the events occur. P(A and B and C) = P(A)P(B|A)P(C|A and B)