Identify the odd one: 2, 3, 5, 7, 11, 13, 17, 20

Question

Identify the odd one:

2, 3, 5, 7, 11, 13, 17, 20

1. A. 17
2. B. 13
3. C. 20 (Correct answer)
4. D. 11

Correct Answer

Option C — 20

Detailed Solution & Explanation

The correct answer is 20.

Key Points

• The list 2, 3, 5, 7, 11, 13, 17 is all prime numbers; 20 = 2² × 5 is composite, so it breaks the rule and is the odd one out.
• When a numeric odd-one-out mixes small integers, test the classic property first — primality.
• Every value but 20 has exactly two factors, which isolates 20 immediately.