Odd One Out — For the pairs (9, 49), (13, 121), (10, 61), (7, 25), choose the only pair that mixes an even number with an odd number.

Introduction / Context:Parity (even vs odd) is a fundamental classification tool. Three pairs are odd–odd; one is even–odd.

Given Data / Assumptions:

• (9, 49): both odd.
• (13, 121): both odd (121 = 11^2).
• (7, 25): both odd.
• (10, 61): 10 is even, 61 is odd.

Concept / Approach:Identify the pair whose members have different parity.

Step-by-Step Solution:Check each pair’s parity: odd–odd, odd–odd, even–odd, odd–odd.The single even–odd mix is (10, 61).

Verification / Alternative check:Other traits (e.g., perfect squares present) do not yield a unique outlier here because multiple pairs include squares. Parity isolates one pair cleanly.

Why Other Options Are Wrong:

• (9, 49): odd–odd.
• (13, 121): odd–odd.
• (7, 25): odd–odd.

Common Pitfalls:Overlooking that 121 is odd even though it is a square; all odd squares remain odd.

Final Answer:10, 61