Classification – Odd one out (multiples of 11) Three of the following integers are exact multiples of 11. Identify the number that is not a multiple of 11 and mark it as the odd one out.

Introduction / Context:
Recognizing multiples of 11 can be done by memory for common values or by using quick division. Many test items include three clean multiples and a single non-multiple to create a unique outlier.

Given Data / Assumptions:

• Candidates: 572, 671, 264, 427
• Property checked: divisibility by 11

Concept / Approach:
Use direct division or recall: 11 * 24 = 264, 11 * 52 = 572, 11 * 61 = 671. If three values match, the leftover is the non-multiple.

Step-by-Step Solution:
264 = 11 * 24 → multiple.572 = 11 * 52 → multiple.671 = 11 * 61 → multiple.427 / 11 = 38 remainder 9 → not a multiple.

Verification / Alternative check:
Applying the alternating-sum rule for 11 also works, but direct factor matches already confirm the classification.

Why Other Options Are Wrong:

• 264: Clean multiple of 11.
• 572: Clean multiple of 11.
• 671: Clean multiple of 11.
• None of these: There is exactly one non-multiple (427).

Common Pitfalls:
Overlooking that 671 is 11 * 61 due to unfamiliarity with larger 11-tables. Memorizing a few key anchors helps.

Final Answer:
427