Classification – Odd one out (multiple of 10 vs non-multiple) Three of the following integers end with 0 and are multiples of 10 (and therefore of 5). Identify the single number that is not a multiple of 10 and mark it as the odd one out.

Introduction / Context:
Many odd-one-out items reward quick recognition of terminal-digit patterns. A number ending with 0 is a multiple of 10 by definition, and hence also a multiple of 5. When three members of a set clearly satisfy this condition and one does not, the decision is immediate. This exercise measures whether you can prioritize the most decisive tests first.

Given Data / Assumptions:

• Set: 120, 168, 290, 380
• We look for the lone non-multiple of 10.

Concept / Approach:
Apply the last-digit test for 10: a number is a multiple of 10 if and only if its last digit is 0. Verify each option and note which one fails this criterion. As a cross-check, recall that multiples of 10 are also even and end specifically with 0 (not merely any even digit).

Step-by-Step Solution:
120 → ends with 0 → multiple of 10.290 → ends with 0 → multiple of 10.380 → ends with 0 → multiple of 10.168 → ends with 8 → not a multiple of 10.

Verification / Alternative check:
You can also reason via factorization: any multiple of 10 must contain a factor 2 and a factor 5. While 168 is even (contains factor 2), it does not contain a factor 5; therefore, it cannot be divisible by 10. The others trivially contain both due to ending in 0.

Why Other Options Are Wrong:

• 120: Multiple of 10 → fits the majority pattern.
• 290: Multiple of 10 → fits the majority pattern.
• 380: Multiple of 10 → fits the majority pattern.
• None of these: There is a single clear non-multiple of 10 (168), so this choice is incorrect.

Common Pitfalls:
Confusing “even” with “multiple of 10.” Not all even numbers are multiples of 10; the last digit must be 0 for divisibility by 10.

Final Answer:
168