In the following list of two letter combinations MN, NM, OL and ET, which pair of letters is the odd one out based on the numerical positions of the letters in the English alphabet?

Introduction / Context:
This question is about finding the odd pair of letters from the given combinations. Instead of numbers, we work with alphabet positions. Such questions check your ability to translate letters into their numerical positions in the alphabet and then look for a consistent numerical pattern.

Given Data / Assumptions:
The given two letter combinations are:

• MN
• NM
• OL
• ET

We assume that exactly one pair does not satisfy the same numerical relationship between the positions of its letters.

Concept / Approach:
The English alphabet positions are A = 1, B = 2, ..., Z = 26. A useful idea here is to add the positions of the two letters in each pair and see whether most of the sums are the same. The pair whose sum is different from the common value is the odd one out.

Step-by-Step Solution:
Step 1: Find the alphabetical positions of each letter.M is the 13th letter and N is the 14th letter, so MN has positions 13 and 14.Step 2: Compute the sum for MN: 13 + 14 = 27.Step 3: For NM, the letters are N (14) and M (13), giving 14 + 13 = 27 again.Step 4: For OL, O is 15 and L is 12, giving 15 + 12 = 27.Step 5: For ET, E is 5 and T is 20, giving 5 + 20 = 25.Step 6: We see that MN, NM and OL all have letter position sums equal to 27, but ET has a sum equal to 25.

Verification / Alternative check:
You can verify by listing the three pairs MN, NM and OL as mirror pairs around the middle of the alphabet because their positions always add up to 27. For example, the pair (13, 14) is just reversed in NM. ET does not share this mirror sum, and 25 is clearly distinct from 27. This reinforces that ET is the only pair not following the same rule.

Why Other Options Are Wrong:
MN, NM and OL all belong to the special group of letter pairs whose positions add up to 27. Removing any of them as the odd one would ignore this neat and consistent property. Therefore, they should be considered similar, and ET should be singled out as different.

Common Pitfalls:
Some learners may search for patterns like letters being consecutive, reversed or symmetric, and overlook the simple and very strong pattern in the sums of positions. Whenever you see letter pairs, checking position sums is a powerful and quick technique to find the odd one out.

Final Answer:
The pair of letters that does not follow the common sum of positions pattern is ET.