Find the odd set: In each triple (a, b, c), the largest number should equal the sum of the other two (largest = sum of smaller two). Identify the set that does NOT follow this rule.

Introduction / Context:
This classification problem uses an additive relation inside triples. The rule: in each triple, the largest member must equal the sum of the other two. One triple fails to meet this requirement; that is the odd set you must identify.

Given Data / Assumptions:

• Triples: (2, 15, 13), (7, 12, 4), (4, 15, 11), (6, 18, 12).
• Assume standard integer arithmetic.

Concept / Approach:
For each triple, sort or mentally identify the largest value, then verify largest = sum of the other two. If equality fails, that triple is the odd one out.

Step-by-Step Solution:

Verification / Alternative check:
Re-express as largest − (sum of others) should equal 0. Only the second triple yields 12 − (7 + 4) = 1 ≠ 0, confirming the violation.

Why Other Options Are Wrong:
They satisfied the additive identity exactly and thus are not the odd item.

Common Pitfalls:
Picking the wrong largest element or mis-adding small numbers under time pressure. Always identify the maximum first, then add carefully.

Final Answer:
7, 12, 4 is the odd set.