The basic rules of probability are:The addition rule will apply when there is a union of 2 other events. Suppose A and B are two events, then:P(A∪B ) = P(A) + P(B) − P(A∩B)The complementary rule will apply whenever an event is a complement of another event. Let A be the event whose complement is to be found:P(A̅) = 1 – P(A)The conditional probability is applied whenever partial knowledge about an event is available. Let A be the event known, and the probability of B is desired, then:P(B/A) = P(A∩B)/P(A)The multiplication rule is applied whenever an event is an intersection of two other events. Suppose A and B occur simultaneously, then:P(A∩B) = P(B) ⋅ P(A|B)