For mutually exclusive events, which formula gives P(A or B)?

For mutually exclusive events, which formula gives P(A or B)?

• A. P(A) + P(B)
• B. P(A) × P(B)
• C. P(A ∩ B)
• D. P(A|B)

Answer: (A)

When two events cannot happen at the same time, the chance that either one occurs is just the sum of their probabilities. That’s because there’s no overlap to worry about, so you don’t double-count any outcomes. The general rule for P(A ∪ B) is P(A) + P(B) − P(A ∩ B). Since they’re mutually exclusive, P(A ∩ B) is zero, so it reduces to P(A) + P(B). The other expressions don’t describe the union: multiplying probabilities gives the chance both happen (which isn’t the same as “either”), and a conditional probability or the intersection probability isn’t what you’re seeking here.

When two events cannot happen at the same time, the chance that either one occurs is just the sum of their probabilities. That’s because there’s no overlap to worry about, so you don’t double-count any outcomes. The general rule for P(A ∪ B) is P(A) + P(B) − P(A ∩ B). Since they’re mutually exclusive, P(A ∩ B) is zero, so it reduces to P(A) + P(B). The other expressions don’t describe the union: multiplying probabilities gives the chance both happen (which isn’t the same as “either”), and a conditional probability or the intersection probability isn’t what you’re seeking here.