In the sequence C L R T B Q S M A P D I N F J K G Y X, certain three letter groups are formed: LBT, IJF, PID and BMS. Four of these five style groups follow a common pattern based on the positions of their letters in the given sequence. Which one of the given groups does NOT belong to this pattern based group?

Introduction / Context:
This question belongs to the “odd one out” type under alphabet test reasoning. You are given a fixed letter sequence and several three letter groups derived from it. Most of these groups follow the same positional pattern, but one group breaks the pattern. You must identify this exceptional group. Such questions check your ability to notice regularities in numeric positions and recognise a break in the pattern among otherwise similar looking options.

Given Data / Assumptions:
1) The fixed sequence is C L R T B Q S M A P D I N F J K G Y X.2) The candidate groups are LBT, IJF, PID and BMS.3) We assume that positions are counted from left to right starting at 1.4) Exactly one of the groups does not follow the same positional rule as the others.

Concept / Approach:
The strategy is to first number the letters of the base sequence, then for each three letter group determine the position of each letter in that sequence. Next, examine differences between positions for each group and compare patterns across groups. If three of the groups show the same numeric relation between positions, that relation forms the rule. The remaining group, which fails to fit the rule, is the odd one out. This positional analysis is more reliable than trying to guess based on letter shapes or meanings.

Step-by-Step Solution:
1) Number the base sequence: 1 C, 2 L, 3 R, 4 T, 5 B, 6 Q, 7 S, 8 M, 9 A, 10 P, 11 D, 12 I, 13 N, 14 F, 15 J, 16 K, 17 G, 18 Y, 19 X.2) For LBT, positions are: L at 2, B at 5, T at 4, so the pattern is 2, 5, 4.3) For IJF, positions are: I at 12, J at 15, F at 14, giving 12, 15, 14.4) For PID, positions are: P at 10, I at 12, D at 11, giving 10, 12, 11.5) For BMS, positions are: B at 5, M at 8, S at 7, giving 5, 8, 7.6) Now look at differences. In LBT, the second position is 3 more than the first (2 to 5), and the third is 1 less than the second (5 to 4).7) In IJF, the second is again 3 more than the first (12 to 15), and the third is 1 less than the second (15 to 14).8) In BMS, the second is 3 more than the first (5 to 8), and the third is 1 less than the second (8 to 7).9) In PID, however, the second is only 2 more than the first (10 to 12), and the third is still 1 less than the second (12 to 11). Thus, the first difference pattern is different here.

Verification / Alternative check:
Summarise the differences for each group: LBT has +3, −1; IJF has +3, −1; BMS also has +3, −1; PID alone has +2, −1. Since three groups consistently follow the rule “second letter is 3 positions ahead of the first, third letter is 1 position behind the second”, while PID does not, PID stands out as the group that breaks the pattern. Checking for any alternative explanations, such as alphabetical distance or other pairings, still shows PID as the unique exception under the positional rule derived from the base sequence.

Why Other Options Are Wrong:
BMS exhibits the same +3, −1 position pattern as LBT and IJF, so it belongs to the main group.LBT fits the rule and is not an exception.IJF also fits the same pattern and therefore is not the odd one out.None of these is incorrect because one of the groups, PID, clearly differs from the others.

Common Pitfalls:
Some candidates look only at the letters themselves and try to find patterns in letter shapes or sounds rather than positions in the given sequence. Others compute differences incorrectly or forget that the rule must be consistent across three of the four options. There is also a temptation to guess rather than carefully calculate. To avoid such mistakes, always write down the positions clearly, compute numeric differences systematically and confirm that the majority of options share a single consistent rule before identifying the outlier.

Final Answer:
The group that does not follow the common positional pattern and is therefore the odd one out is PID.