Events A and B are independent with P(A) = 2/5 and P(B) = 1/4. What is the probability that at least one of them occurs?
Answer and explanation
Correct answer: D. 11/20
- Step 1: P(A and B) = 2/5 x 1/4 = 1/10. Step 2. P(A or B) = P(A) + P(B) - P(A and B) = 2/5 + 1/4 - 1/10 = 11/20. Answer: 11/20. Why not the others: 13/20: That adds the probabilities and counts the overlap twice. 1/10: That is the probability that both occur. 3/10: That is the probability that A occurs and B does not.
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