In this number pair reasoning question, each option shows a pair in the form a–b: 73–61, 57–69, 47–59 and 42–29. Select the odd pair that does not follow the same pattern as the others.

Introduction / Context:
This question tests your ability to spot a simple arithmetic relationship between two numbers in a pair. The given pairs are 73–61, 57–69, 47–59 and 42–29. In three of these pairs, the difference between the two numbers has the same magnitude. One pair has a different difference and is therefore the odd one out. This is a common style of question in basic aptitude tests.

Given Data / Assumptions:

• Number pairs: 73–61, 57–69, 47–59 and 42–29.
• We are interested in the absolute difference between the two numbers in each pair.
• In three pairs, this difference is equal to 12.
• Exactly one pair has a different difference and must be identified.

Concept / Approach:
We compute b - a or a - b for each pair and focus on the absolute value of the difference. If three differences have the same magnitude, that forms the main pattern. The fourth pair, whose difference magnitude is different, is the odd one out. This approach does not require any advanced mathematics, only basic subtraction.

Step-by-Step Solution:
Step 1: Calculate the difference for 73–61.73 - 61 = 12. The absolute difference is 12.Step 2: Calculate the difference for 57–69.69 - 57 = 12. Again, the absolute difference is 12.Step 3: Calculate the difference for 47–59.59 - 47 = 12. So this pair also has an absolute difference of 12.Step 4: Calculate the difference for 42–29.42 - 29 = 13. Here the absolute difference is 13, which does not match the other three pairs.Step 5: Identify the odd pair.Since 73–61, 57–69 and 47–59 all have a difference of 12, and 42–29 has a difference of 13, 42–29 is the odd one out.

Verification / Alternative check:
You can verify this pattern quickly by writing each pair in ascending order and then subtracting the smaller number from the larger one. Doing so gives you 73–61, 69–57, 59–47 and 42–29. The resulting differences are 12, 12, 12 and 13. Seeing three equal differences and one different value makes it obvious which pair does not belong with the others. This method is especially useful in time bound exams where speed matters.

Why Other Options Are Wrong:
73–61: The difference is exactly 12, so it follows the main pattern.
57–69: The difference is also 12, consistent with the first pair.
47–59: Again yields a difference of 12 and fits the same relationship.

Common Pitfalls:
Some candidates may try to interpret the numbers as primes or composites and search for more difficult patterns. While 73, 61, 47 and 59 are primes and 57 and 69 are not, the question here is only about the relationship within each pair, not about prime status. Always read the question carefully and look for the simplest numerical link first, such as sum, difference or product, before exploring more complex interpretations.

Final Answer:
The odd pair is 42–29, because its difference is 13, while the difference for each of the other three pairs is 12.