Classification – Odd one out (perfect squares) Three of the following numbers are perfect squares. Identify the number that is not a perfect square and mark it as the odd one out.

Introduction / Context:
Perfect squares are common anchors in classification puzzles. Rapid recognition of standard squares (12^2 = 144, 13^2 = 169, 18^2 = 324) allows you to isolate a non-square quickly, which is often the intended odd element in such sets.

Given Data / Assumptions:

• Candidates: 144, 169, 288, 324
• Target: find the unique non-square.

Concept / Approach:
Compare each value to nearby known squares and confirm exact equality. If a number sits strictly between two consecutive squares, it cannot be a perfect square. This method avoids unnecessary root calculations.

Step-by-Step Solution:
144 = 12^2 → square.169 = 13^2 → square.324 = 18^2 → square.288 lies between 16^2 = 256 and 17^2 = 289, and is not equal to either → not a square.

Verification / Alternative check:
Square-root estimate: sqrt(288) ≈ 16.97, not an integer. Therefore 288 is not a perfect square, while the others match exact k^2 values.

Why Other Options Are Wrong:

• 144: Exact square.
• 169: Exact square.
• 324: Exact square.
• None of these: The unique non-square is 288.

Common Pitfalls:
Believing that proximity to a square implies squareness. Only exact equality to k^2 counts.

Final Answer:
288