Answer: The Addition Rule for disjoint events is the sum of the probabilities of 2 events, while the General Addition Rule says if 2 are disjoint, then the probability of either event is the sum of the probabilities of the two events: P(A or B) = P(A) + P(B).
Step-by-step explanation: The Addition Rule states that for two disjoint events, the probability that one or the other occurs is the sum of the probabilities of the two events. (Book example on p. 280 about the probability that a randomly selected student is either a sophomore (A) or a junior (B) therefore P(A or B). The addition of probabilities for disjoint events is the third basic rule of probability: Rule 3: If two events A and B are disjoint, then the probability of either event is the sum of the probabilities of the two events: P(A or B) = P(A) + P(B).