Identify the odd number: Among 31, 39, 47, and 41, three are prime; one is composite. Choose the composite number.

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:

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.