Classification (number pairs – square roots): Three pairs show perfect squares where the second equals the square root of the first; one pair is not a perfect square relation. Identify the odd pair.

Introduction / Context:
Another common numeric classification relies on perfect squares. When a pair is presented as (A, B), many items use the rule B = sqrt(A). Fast recognition of perfect squares saves time and reduces errors in competitive tests. Your task is to detect the pair that fails to meet this square root relation.

Given Data / Assumptions:

• Pairs: 64-8, 36-6, 49-7, 80-9.
• Known squares: 8^2 = 64, 6^2 = 36, 7^2 = 49.
• Check whether 9^2 = 81, which would be required for 80-9 to fit the pattern.

Concept / Approach:
Compute the square of the second number for each pair and compare it to the first. If A equals B^2, the pair fits. Otherwise, it is the exception. Memorizing squares up to 20 accelerates this process.

Step-by-Step Solution:

Verification / Alternative check:
Reverse check by taking sqrt(64)=8, sqrt(36)=6, sqrt(49)=7. For 80, the square root is not an integer (approximately 8.944...). Therefore, 80-9 is not a perfect square pair.

Why Other Options Are Wrong:

Common Pitfalls:
Rounding errors or estimating roots without confirming. Always verify by squaring the second number to see if it exactly equals the first.

Final Answer:
80-9