Find the odd number pair from the following alternatives based on the constant difference between the two numbers.

Introduction / Context:
This number pair question checks whether you can recognize a constant difference pattern between two numbers. Three pairs share the same difference and one pair has a different difference, making it the odd one out.

Given Data / Assumptions:

• Pairs: 8 - 11, 1 - 4, 7 - 10, 3 - 5.
• We examine the difference between the second and first number in each pair.
• We look for a simple constant difference like +3 or +2.

Concept / Approach:
The concept is straightforward. For each pair, subtract the first number from the second number. If three pairs show the same difference and one pair shows a different difference, the latter pair is the odd one. This is a very common pattern in introductory reasoning questions.

Step-by-Step Solution:
8 - 11: 11 - 8 = 3. 1 - 4: 4 - 1 = 3. 7 - 10: 10 - 7 = 3. 3 - 5: 5 - 3 = 2. Thus three pairs have a difference of 3, while one pair has a difference of 2.

Verification / Alternative check:
You can also think of each pair as a mini arithmetic progression. 8, 11; 1, 4; and 7, 10 all rise by 3. The pair 3, 5 rises only by 2. Since a consistent common difference is often the intended rule in such problems, the pair with a different common difference is the odd one.

Why Other Options Are Wrong:

• 8 - 11: Follows the +3 difference and matches 1 - 4 and 7 - 10.
• 1 - 4: Another example of the +3 step between numbers.
• 7 - 10: Also shows the same +3 difference.

Common Pitfalls:
This question is simple, but under time pressure, students may attempt to find more complex patterns and miss the obvious constant difference. In many exam problems, the simplest arithmetic relation is the intended one, so always check addition and subtraction patterns first.

Final Answer:
3 - 5