If A and B are mutually exclusive, P(A or B) equals?

• A. P(A) × P(B)
• B. P(A) - P(B)
• C. P(A) + P(B)
• D. P(A^c) + P(B^c)

Answer: (C)

When two events cannot happen at the same time, the probability that at least one of them occurs is the sum of their individual probabilities. This is because the union probability is P(A ∪ B) = P(A) + P(B) − P(A ∩ B), and for mutually exclusive events the intersection probability is zero, so it simplifies to P(A) + P(B).

The other forms don’t represent the chance of either event occurring. P(A) × P(B) would reflect a joint probability under a different assumption (not applicable here since A and B can’t both happen). Subtracting P(B) from P(A) gives a different quantity altogether. Adding the complements, P(A^c) + P(B^c), does not equal the probability of A or B (it equals 2 − [P(A) + P(B)] in general).