Mutually Exclusive Events
Last topic, you learned how to find the probability of two events, A and B, occurring in sequence. Such probabilities are denoted by P(A and B).
In this topic, you will learn how to find the probability that at least one of two events will occur. Probabilities such as these are denoted by P(A or B) and depend on whether the events are mutually exclusive.
In words, to find the probability that one event or the other will occur, add the individual probabilities of each event and subtract the probability that they
both occur. As shown in the Venn diagram at the left, subtracting P1A and B2 avoids double counting the probability of outcomes that occur in both A and B.