Classification – Odd one out (divisibility by 3) Exactly one of the following four-digit numbers is not divisible by 3. Identify the number that fails the divisibility-by-3 test and mark it as the odd one out.

Introduction / Context:
Divisibility rules provide the fastest route in many classification questions. For 3, the rule is: a number is divisible by 3 if the sum of its digits is divisible by 3.

Given Data / Assumptions:

• Options: 1236, 2346, 4566, 5686
• We will apply the digit-sum test.

Concept / Approach:
Compute the digit sum for each option and test divisibility by 3.

Step-by-Step Solution:
1236 → 1 + 2 + 3 + 6 = 12 → divisible by 3.2346 → 2 + 3 + 4 + 6 = 15 → divisible by 3.4566 → 4 + 5 + 6 + 6 = 21 → divisible by 3.5686 → 5 + 6 + 8 + 6 = 25 → not divisible by 3.

Verification / Alternative check:
Trial division by 3 confirms a remainder for 5686 and no remainder for the others.

Why Other Options Are Wrong:

• 1236: Divisible by 3.
• 2346: Divisible by 3.
• 4566: Divisible by 3.
• None of these: There is one clear non-multiple (5686).

Common Pitfalls:
Confusing “ends with 6” as implying divisibility by 3. The last digit does not determine divisibility by 3; only the digit sum matters.

Final Answer:
5686