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

• A. P(A)P(B)
• B. P(A) + P(B)
• C. P(A) - P(B)
• D. max(P(A), P(B))

Answer: (B)

Mutually exclusive means A and B cannot occur at the same time, so their intersection has probability zero. The general formula for the probability of A or B is P(A ∪ B) = P(A) + P(B) − P(A ∩ B). Since P(A ∩ B) = 0 in this case, it simplifies to P(A) + P(B). Therefore, the probability of A or B equals the sum of their probabilities.

The other options don’t fit because they imply different relationships: the product would be the probability of both occurring under certain conditions (like independence), which isn’t possible here; subtracting would miscount the overlap; taking the maximum wouldn’t generally give the union probability.