In the following question, four letter groups are given: IMX, DHS, GWK and KOZ. In three of these groups, the letters follow the pattern of jumping +4 positions and then +11 positions in the English alphabet, while one group does not follow this pattern. Which letter group is the odd one out?

Introduction / Context:
This question comes from the letter series and odd one out section of aptitude tests. You are given four three-letter groups and must identify which one does not follow the same pattern in terms of letter positions in the English alphabet. Such questions strengthen your skill in translating letters to numbers (A = 1 to Z = 26) and spotting arithmetic patterns in the jumps between letters.

Given Data / Assumptions:

• Letter groups: IMX, DHS, GWK, KOZ.
• Alphabet positions: A = 1, B = 2, ..., Z = 26.
• We will check the position differences between consecutive letters in each group.
• We expect three groups to share a common pattern and one group to differ.

Concept / Approach:
A standard approach is to compute the difference in positions between the first and second letters, and between the second and third letters. When a clear pattern such as +4, +11 appears repeatedly, we can classify groups that follow this pattern together and then identify the one that does not. The group breaking the pattern is the odd one out.

Step-by-Step Solution:
Step 1: For IMX: I = 9, M = 13, X = 24. Differences: M - I = 13 - 9 = 4, X - M = 24 - 13 = 11. So the pattern is +4, then +11. Step 2: For DHS: D = 4, H = 8, S = 19. Differences: H - D = 8 - 4 = 4, S - H = 19 - 8 = 11. Again, the pattern is +4, then +11. Step 3: For KOZ: K = 11, O = 15, Z = 26. Differences: O - K = 15 - 11 = 4, Z - O = 26 - 15 = 11. This also follows the +4, then +11 pattern. Step 4: For GWK: G = 7, W = 23, K = 11. Differences: W - G = 23 - 7 = 16, K - W = 11 - 23 = -12. Step 5: The pattern in GWK, with jumps of +16 and -12, clearly does not match the neat +4, +11 pattern of the other three letter groups. Step 6: Therefore, GWK is the odd one out.

Verification / Alternative check:
As a quicker check, you can visually inspect whether the letters look evenly spaced in the alphabet. IMX, DHS and KOZ all show moderately spaced jumps that are consistent in size, while GWK contains a very large jump from G to W and then backwards from W to K. This visual irregularity indicates GWK behaves differently, confirming our detailed numeric analysis.

Why Other Options Are Wrong:
IMX is not odd because the differences between its letters are +4 and +11, matching the common pattern. DHS is not odd because it also follows +4 and +11 between consecutive letters. KOZ is not odd because it continues the exact same +4 and +11 jump pattern. Only GWK fails to follow this jump pattern, showing irregular jumps of +16 and -12.

Common Pitfalls:
Students sometimes miscalculate letter positions or forget that Z corresponds to 26, leading to incorrect differences. Another pitfall is looking only at increasing or decreasing sequences without checking actual jump sizes. To avoid such mistakes, always write down the position numbers and perform basic subtraction carefully.

Final Answer:
The letter group that does not follow the +4, then +11 pattern and is therefore the odd one out is GWK.