Classification – Odd one out (multiples of 7) Three of the following integers are clean multiples of 7. Identify the number that is not a multiple of 7 and mark it as the odd one out.

Introduction / Context:
Multiples of a small prime such as 7 are common in classification exercises. Faster solutions come from either recalling times-table anchors or performing small divisions without long arithmetic.

Given Data / Assumptions:

• Candidates: 28, 35, 42, 65
• Property in focus: divisibility by 7

Concept / Approach:
Check each candidate by quick division or factor recall. 28 = 7 * 4, 35 = 7 * 5, 42 = 7 * 6 are well-known. The remaining value should fail the 7-multiple test to become the odd one out.

Step-by-Step Solution:
28 → 7 * 4 → multiple of 7.35 → 7 * 5 → multiple of 7.42 → 7 * 6 → multiple of 7.65 ÷ 7 = 9 remainder 2 → not a multiple of 7.

Verification / Alternative check:
Prime-factor view: 65 = 5 * 13 contains no factor 7, confirming it is the outlier.

Why Other Options Are Wrong:

• 28: Multiple of 7.
• 35: Multiple of 7.
• 42: Multiple of 7.
• None of these: A single non-multiple exists (65).

Common Pitfalls:
Assuming “ends with 5” automatically signals special status. Ending with 5 relates to divisibility by 5, not by 7; always test the actual target factor.

Final Answer:
65