Difficulty: Medium
Correct Answer: 78
Explanation:
Introduction / Context:
Several classification items rely on a specific hidden factor. Here, we test for the presence of the prime 13 in the factorization.
Given Data / Assumptions:
Concept / Approach:
Factor each number or check divisibility by 13. Because 13 * 6 = 78, this quickly singles out the outlier.
Step-by-Step Solution:
Verification / Alternative check:
Dividing each by 13: only 78/13 = 6 is integer; others are not.
Why Other Options Are Wrong:
48, 72, and 54 share small prime factors 2 and 3 but lack 13.
Common Pitfalls:
Using only parity or sum-of-digits rules; those do not detect the presence of 13.
Final Answer:
78 is the only number with prime factor 13 and is the odd number.
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