Addition and Multiplication Rules for Probability

Two events are mutually exclusive events if they cannot occur at the same time or they have no outcomes in common and if they cannot occur at the same time they are not mutually exclusive events.

ADDITION RULE

Addition rule 1: When 2 events A and B are mutually exclusive, the probability that A or B occurs is

P(A or B)=P(A)+P(B)

Addition rule 2: When 2 events A and B are not mutually exclusive then,

P(A or B)=P(A)+P(B)-P(A and B)

MULTIPLICATION RULE

Two events A and B are Independent events if the fact that A occurs does not affect the probability of B occurring.

P(A and B)=P(A)xP(B)

When an occurrence or outcome of the first event affects the occurrence or outcome of the second event in such a way that the probability is changed, the events are said to be dependent.

P(A and B)=P(A)xP(A/B)






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