From 13 applicants (5 women, 8 men), two persons are selected at random. What is the probability that at least one selected person is a woman?
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A25/39
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B14/35
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C5/13
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D10/13
Answer
Correct Answer: 25/39
Explanation
Introduction / Context:“At least one” probability questions are usually simpler via complement: subtract the probability that no one satisfies the property from 1. Here, “no woman” means both selected are men.
Given Data / Assumptions:
- Total applicants = 13 (5 women, 8 men).
- Two are selected uniformly without order.
Concept / Approach:P(≥1 woman) = 1 − P(both men) = 1 − C(8,2)/C(13,2).
Step-by-Step Solution:C(8,2) = 28; C(13,2) = 78.P(≥1 woman) = 1 − 28/78 = 50/78 = 25/39.
Verification / Alternative check:Direct count of favourable outcomes: total pairs (78) minus all-men pairs (28) = 50 favourable → 50/78 = 25/39.
Why Other Options Are Wrong:10/13 and 5/13 arise from incorrect linear approximations; 14/35 is unrelated.
Common Pitfalls:Forgetting to use combinations (unordered selection) or to apply the complement method.
Final Answer:25/39