To find the probability of the union of two events A and B (denoted as P(A ∪ B)), use the formula:
P(A ∪ B) = P(A) + P(B) – P(A ∩ B).

This formula accounts for the overlap between the two events so that it is not counted twice. If A and B are mutually exclusive (cannot happen together), then P(A ∩ B) = 0, and the formula becomes P(A ∪ B) = P(A) + P(B).