Choose the odd letter-triplet: In each three-letter group, check the movement in the English alphabet from the 1st to the 2nd letter and from the 2nd to the 3rd letter. Three groups follow the fixed pattern “+3 then -5” (forward by 3 positions, then backward by 5). Identify the group that does not follow this pattern.

Introduction / Context:
Letter-classification questions commonly encode arithmetic jumps on alphabet positions (A=1, B=2, …, Z=26). Here, the governing pattern is “+3 then -5” across each three-letter group. We must find the set that fails the rule.

Given Data / Assumptions:

• Alphabet indices: A=1 … Z=26.
• Groups: LOJ, FID, RUP, ILN.
• Target rule: first→second = +3; second→third = -5.

Concept / Approach:
Translate letters to indices, apply the difference check (+3, then -5), and flag any violation. Wrap-around is not required here because all letters remain within A–Z bounds.

Step-by-Step Solution:

Verification / Alternative check:
Reverse-check by recomputing: only ILN shows +3 followed by +2, not -5, so it breaks the rule.

Why Other Options Are Wrong:
LOJ, FID, and RUP implement the exact +3 then -5 transitions.

Common Pitfalls:
Counting letter positions off by one or forgetting that J=10, N=14, etc. Always map letters to numbers before comparing.

Final Answer:
ILN is the odd triplet because it violates the “+3 then -5” pattern.