Addition Rule of Probability
The addition rule finds the probability that event A or event B occurs. When the events overlap, subtract the overlap so it isn't counted twice:
P(A or B) = P(A) + P(B) − P(A and B)
When A and B are mutually exclusive (they can never happen together), P(A and B) = 0, so the rule simplifies to P(A or B) = P(A) + P(B).
Practice: Addition Rule of Probability
Apply the addition rule for overlapping or mutually exclusive events.