Identify the odd number: Among 31, 39, 47, and 41, three are prime; one is composite. Choose the composite number.
Verbal Reasoning
Classification
Difficulty: Easy
Choose an option
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A31
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B39
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C47
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D41
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ENone of these
Answer
Correct Answer: 39
Explanation
Introduction / Context:Prime recognition is central to numeric classification. Only one selection is composite.
Given Data / Assumptions:
- Set: 31, 39, 47, 41.
- Definition: prime has exactly two positive divisors.
Concept / Approach:Apply small-prime divisibility tests, especially 3 and 5 for quick screening.
Step-by-Step Solution:
31 → not divisible by 2, 3, 5 → prime.39 → 3 + 9 = 12 → divisible by 3 → composite.47 → not divisible by 2, 3, 5 → prime.41 → not divisible by 2, 3, 5 → prime.Verification / Alternative check:Direct factorization: 39 = 3 * 13 confirms compositeness.
Why Other Options Are Wrong:31, 47, 41 are primes.
Common Pitfalls:Confusing proximity to a multiple of 3 with actual divisibility.
Final Answer:39 is the composite number and the odd one out.