Classification – Odd one out (divisibility by 3) Three of these four-digit numbers are not divisible by 3, while exactly one is divisible by 3. Identify the multiple of 3 and mark it as the odd one out.

Introduction / Context:
Digit-sum divisibility is a staple in reasoning tests. For 3, a number is divisible if its digit sum is a multiple of 3. Here, exactly one value meets this rule, making it the odd one out.

Given Data / Assumptions:

• Candidates: 3216, 2338, 3205, 2015
• Property checked: divisibility by 3 using digit-sum

Concept / Approach:
Compute digit sums and check membership in {0, 3, 6, 9, 12, …}. Only the number with a digit sum divisible by 3 is a multiple of 3.

Step-by-Step Solution:
3216 → 3 + 2 + 1 + 6 = 12 → divisible by 3.2338 → 2 + 3 + 3 + 8 = 16 → not divisible by 3.3205 → 3 + 2 + 0 + 5 = 10 → not divisible by 3.2015 → 2 + 0 + 1 + 5 = 8 → not divisible by 3.

Verification / Alternative check:
Direct division: 3216/3 = 1072 (integer). The others leave remainders upon division by 3.

Why Other Options Are Wrong:

• 2338: Fails digit-sum test.
• 3205: Fails digit-sum test.
• 2015: Fails digit-sum test.
• None of these: There is one clear multiple of 3 (3216).

Common Pitfalls:
Judging by evenness or size instead of using the correct rule. Only the digit-sum test matters for 3.

Final Answer:
3216