In this letter-pattern reasoning question, select the odd group of letters from the following alternatives: CEAC, FHDF, PRMP, TVRT.

Introduction / Context:
This question belongs to the letter sequence and pattern recognition category of aptitude tests. The groups of letters given are CEAC, FHDF, PRMP and TVRT. You must identify which group does not follow the same positional rule as the others. Such problems strengthen your skills in working with alphabetical positions and detecting hidden rules in letter arrangements.

Given Data / Assumptions:

• Letter groups: CEAC, FHDF, PRMP, TVRT.
• We use alphabetical positions: A = 1, B = 2, ..., Z = 26.
• Each group consists of four letters, and we expect a consistent pattern in three of them.
• Exactly one group will break that pattern and will be the odd one out.

Concept / Approach:
The best approach is to convert letters into their numeric positions and compare the differences between consecutive letters inside each group. If three groups follow the same pattern of differences and one does not, that differing group is the odd one. This is a standard technique in letter analogy and classification questions.

Step-by-Step Solution:
Step 1: Analyze CEAC.C = 3, E = 5, A = 1, C = 3. Differences are: 3 to 5 = +2, 5 to 1 = -4, 1 to 3 = +2. So the pattern is +2, -4, +2.Step 2: Analyze FHDF.F = 6, H = 8, D = 4, F = 6. Differences: 6 to 8 = +2, 8 to 4 = -4, 4 to 6 = +2. Again the pattern is +2, -4, +2.Step 3: Analyze TVRT.T = 20, V = 22, R = 18, T = 20. Differences: 20 to 22 = +2, 22 to 18 = -4, 18 to 20 = +2. The same +2, -4, +2 pattern reappears.Step 4: Analyze PRMP.P = 16, R = 18, M = 13, P = 16. Differences: 16 to 18 = +2, 18 to 13 = -5, 13 to 16 = +3. Here the pattern is +2, -5, +3, which is different from the other three groups.Step 5: Identify the odd group.PRMP alone does not follow the consistent +2, -4, +2 difference pattern and is therefore the odd one out.

Verification / Alternative check:
To verify, you can attempt to reconstruct each group using the discovered pattern. Starting from C, adding 2 gives E, subtracting 4 gives A and adding 2 gives C again, which matches CEAC. Repeating the same logic from F and T also recreates FHDF and TVRT exactly. When you try the same pattern on P, you would expect +2 to R, -4 to N and +2 to P, which would generate the sequence PRNP rather than PRMP. Since PRMP does not arise naturally from the shared pattern, it confirms that PRMP is the inconsistent group.

Why Other Options Are Wrong:
CEAC: Follows the +2, -4, +2 rule perfectly and matches the main pattern of the question.
FHDF: Also follows the same +2, -4, +2 difference pattern and is consistent with CEAC and TVRT.
TVRT: Again fits the same letter movement rule and therefore cannot be the odd one out.

Common Pitfalls:
Some students attempt to find meaning in the groups as abbreviations or words, which is not relevant here. Others compare only the first and last letters without checking the internal pattern. For letter series and classification questions, it is important to systematically convert letters to numbers and analyze the full sequence of differences to uncover the underlying rule.

Final Answer:
The odd group of letters is PRMP, because it does not follow the +2, -4, +2 pattern that appears in the other three groups.