Odd One Out — In the number pairs 20–36, 30–36, 50–56, and 60–66, pick the pair that does not follow the same constant-difference pattern. Explain the rule you used.

Introduction / Context:
Classification questions on number pairs often rely on a simple arithmetic relation like a constant difference or ratio. The task is to find the one pair that breaks the common rule.

Given Data / Assumptions:

• Pairs provided: 20–36, 30–36, 50–56, 60–66.
• We interpret “a–b” as an ordered pair (a, b) with a simple relation connecting a to b.
• We will test the most economical relation first: constant difference (b − a).

Concept / Approach:
Compute the difference b − a for each pair and compare the results. When three share the same difference and one does not, the odd one is isolated.

Step-by-Step Solution:
For 20–36: difference = 36 − 20 = 16.For 30–36: difference = 6.For 50–56: difference = 6.For 60–66: difference = 6.Observation: three pairs share the same difference (+6). One pair has a larger, different difference (+16).

Verification / Alternative check:
Check ratios quickly: 36/20 = 1.8; 36/30 = 1.2; 56/50 = 1.12; 66/60 = 1.1. Ratios are not equal, so the constant-difference pattern is the most coherent commonality among three pairs.

Why Other Options Are Wrong:

• 30–36: fits b − a = +6.
• 50–56: fits b − a = +6.
• 60–66: fits b − a = +6.

Common Pitfalls:
A frequent mistake is to jump to multiplicative patterns when an additive pattern already cleanly explains three of the four options. Always test simplest invariants (difference, parity) first.

Final Answer:
20-36