Two independent events have probabilities 0.5 and 0.4. What is the probability that at least one occurs?

Answer and explanation

Correct answer: C. 0.7

  1. Step 1: P(at least one) = 1 − P(none) = 1 − (1/2)(0.6). Step 2. = 0.7. Answer: 0.7. Why not the others: 0.2 is what you get if you give the probability that both occur. 0.9 is what you get if you add without subtracting the overlap. 0.3 is what you get if you give the probability that only the first occurs.

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