Choose the odd number: Among 43, 53, 63, and 73, three are prime and one is composite. Identify the composite number.

Introduction / Context:
Most numbers in this set are primes; the single composite is the odd one out.

Given Data / Assumptions:

• Set: 43, 53, 63, 73.
• Primes around 40–80 are commonly tested.

Concept / Approach:
Use digit-sum rule for 3 and quick small-prime checks.

Step-by-Step Solution:

Verification / Alternative check:
Direct division by 7: 63 = 7 * 9 confirms compositeness.

Why Other Options Are Wrong:
They lack non-trivial divisors and are prime.

Common Pitfalls:
Assuming “ends with 3” implies divisibility by 3; the rule concerns digit sums, not the last digit.

Final Answer:
63 is composite and thus the odd number.