Find the odd number out: 3, 5, 7, 12, 13, 17, 19.

Introduction / Context:This set is dominated by primes; a single composite number appears among them. Recognizing small primes (up to about 20) quickly isolates the outlier.

Given Data / Assumptions:

• Primes present: 3, 5, 7, 13, 17, 19
• Composite present: 12 (divisible by 2, 3, 4, 6)

Concept / Approach:Classify each as prime or composite. The composite entry among mostly primes is the odd one out.

Step-by-Step Solution:Check: 12 is composite; all the others listed are prime numbersTherefore, 12 is the odd term

Verification / Alternative check:Trial division confirms primality of 13, 17, 19 and composite nature of 12; 12 = 3*4 = 2*6.

Why Other Options Are Wrong:19/17/13 are prime and belong with the majority of the set.

Common Pitfalls:Mislabeling 1 as prime (not applicable here) or overlooking small composite checks.

Final Answer:12