Probability Rules Judith Alexis Georgina

Rule #1 All probabilities are values between 0 & 1 Example : Which numbers can’t be a probability? % 7/

Rule #2 Sum of probabilities of all outcomes = 1 Sample Space P(S) = 1 Example: M&M percentages equal 100

Rule #3 If 2 events have no outcomes in common (disjoint/mutually exclusive) then the probability of one or the other occurring is the sum of their individual probabilities P(A or B) = P(A) + P (B) Example: You can’t miss a bus & catch a bus at the same time You can’t sit down & stand up at the same time OR

Rule #4 Probability that an event does not occur is one minus the probability that the event will occur ( complement rule) Example: P(person has black hair) = 0.75 so, P (person who does not have black hair) = 1 – 0.75 = 0.25