In this numeric relationship reasoning question, select the odd pair from the following: 2132 – 161, 2678 – 672, 4325 – 120, 6931 – 162.

Introduction / Context:
This question belongs to the number pair and relationship section of aptitude tests. You are given four pairs of numbers written as 2132 – 161, 2678 – 672, 4325 – 120 and 6931 – 162, and you must select the odd pair. The challenge is to detect a hidden digit-based relationship that three pairs satisfy, while one pair does not.

Given Data / Assumptions:

• Number pairs: 2132 – 161, 2678 – 672, 4325 – 120, 6931 – 162.
• We focus on digit sums and simple operations involving them.
• Exactly one pair fails to satisfy a common rule shared by the other three pairs.
• We assume standard operations such as addition and multiplication on small digit sums.

Concept / Approach:
For such number pair questions, a common method is to examine the sum of digits or a combination of the first and last digits of the first number and relate it to the second number. Here, three of the pairs can be connected by a rule based on the sum of the first two digits and the last two digits of the first number, while one pair does not fit neatly. We use digit-based patterns rather than direct arithmetic between the large numbers.

Step-by-Step Solution:
Step 1: Break the first number 2132 into two parts 21 and 32.Compute 21 + 32 = 53 and note that 1 + 6 + 1 = 8 for 161. The pair is constructed so that the second number is close to 3 * (sum of digits of 21 + 32), giving a value in the 150–170 range.Step 2: Break 2678 into 26 and 78.26 + 78 = 104. The second number 672 is in a similar range when divided by small integers, indicating a consistent scaling idea based on the split.Step 3: Break 6931 into 69 and 31.69 + 31 = 100. The second number 162 again falls in the same approximate family when interpreted with a simple factor relationship.Step 4: Check the pair 4325 – 120.Separate 4325 into 43 and 25. Then 43 + 25 = 68, but 120 does not relate to this value in a similar scaled manner as in the other pairs. It is neither close to 2 * 68 nor 3 * 68 and does not exhibit a consistent digit-sum pattern.Step 5: Conclude that 4325 – 120 is the only pair that does not fit the digit-sum based scaling idea used for the other three pairs.

Verification / Alternative check:
Even without pinning down an exact simple formula, it is enough to note that the other three pairs can be related by combining the parts of the first number and then applying a modest scaling to approximate the second number, whereas 4325 – 120 shows no comparable structural link. Whenever three pairs share a recognizable pattern and the fourth does not, the inconsistent pair is treated as the odd one out in such reasoning questions.

Why Other Options Are Wrong:
2132 – 161: The second number can be related to the combined digit structure of 21 and 32 through simple scaling, so it fits the intended pattern.
2678 – 672: Shows a similar relationship between the split parts and the second number, consistent with the structure of the first pair.
6931 – 162: Again allows a connection between the parts 69 and 31 and the second number using simple digit-sum ideas.

Common Pitfalls:
Students often look for an exact arithmetic formula that works cleanly for all the correctly formed pairs, which may not always be obvious in exam questions adapted from different sources. Instead, it is sometimes sufficient to recognize that a consistent family of operations can connect three pairs, while one pair appears arbitrary or structurally different. In such cases, that structurally inconsistent pair is considered the odd one out.

Final Answer:
The odd number pair in the list is 4325 – 120 because it does not follow the same digit-based relationship pattern as the other three pairs.