STA 220 Lecture Notes - Lecture 8: Conditional Probability
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Sta 220 - lecture 8 - chapter 13. When two events a and b are disjoint, we can use the addition rule for disjoint events. P(a or b) = p(a) + p(b) P(a or b) = p(a) + p(b) - p(a and b) 33% are in a fraternity or a sorority. Find the probability that a randomly selected student is in a fraternity/sorority or is involved in sports. P(r or s) = p(r) + p(s) - p(r and s) There is a 47% chance that a randomly selected student is in a fraternity/sorority or is involved in sports. When we want the probability of an event from a conditional distribution, we write: Pronounce it the probability of b given a . A probability that takes into account a given condition is called conditional probability. To find the probability of the event b given the event a, we restrict our attention to the outcomes in a.