CA Foundation · Quantitative Aptitude · Probability
Events A and B are independent with P(A) = 0.6 and P(B) = 0.5. What is the probability that at least one of them occurs?
The probability is 0.80. Since the events are independent, the chance that neither occurs is 0.4 × 0.5 = 0.20, so at least one occurs with probability 1 − 0.20 = 0.80. This matches 0.6 + 0.5 − 0.30.
- A0.30
- B0.70
- C0.80Correct
- D1.10
Explanation
P(A and B) = 0.6 × 0.5 = 0.30. P(A or B) = 0.6 + 0.5 − 0.30 = 0.80. Check: 1 − (0.4 × 0.5) = 0.80. The value 1.10 comes from forgetting to subtract the overlap, and it exceeds 1 so it cannot be a probability.
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