Two candidates A and B interview for two vacancies. The probabilities that A and B are selected are 1/3 and 1/6 respectively. Assuming independence, what is the probability that neither is selected?
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A5/9
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B5/12
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C1/12
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D1/24
Answer
Correct Answer: 5/9
Explanation
Introduction / Context:Given marginal selection probabilities for two candidates and assuming independence of their outcomes, the chance that neither is selected is the product of their non-selection probabilities.
Given Data / Assumptions:
- P(A selected) = 1/3 → P(A not selected) = 2/3.
- P(B selected) = 1/6 → P(B not selected) = 5/6.
- Selections are independent (standard assumption unless stated otherwise).
Concept / Approach:P(neither) = P(A not selected) * P(B not selected).
Step-by-Step Solution:P(neither) = (2/3) * (5/6) = 10/18 = 5/9.
Verification / Alternative check:P(at least one selected) = 1 − 5/9 = 4/9. Inclusion–exclusion also yields P(A ∪ B) = 1/3 + 1/6 − (1/3)(1/6) = 1/2 − 1/18 = 8/18 = 4/9.
Why Other Options Are Wrong:5/12 and smaller values underestimate; independence requires multiplying complements, not adding/subtracting naïvely.
Common Pitfalls:Assuming mutual exclusivity or that exactly two positions force dependence; the statement provides independent success chances for each candidate.
Final Answer:5/9