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Coding-Decoding and Number/Letter Series
Coding-Decoding relies on identifying a consistent transformation rule (shift, reverse, substitute) applied uniformly to every letter of a word. Always verify the rule using at least two letters before applying it to the answer choices. Number/Letter series questions require checking differences, ratios, and squares/cubes systematically — start with simple addition/subtraction, then try multiplication, then higher-order patterns like squares or interleaved series if the simple checks fail.
Important topics
- Letter-shifting code: each letter of the alphabet is shifted forward or backward by a fixed number of positions
- Number coding: letters or words replaced by their positional numbers (A=1, B=2, ... Z=26)
- Reverse coding: letters/words are written in reverse order as the code
- Arithmetic number series: constant or increasing difference, or a fixed multiplier (e.g., ×2, ×2+1)
- Geometric/multiplicative series: each term obtained by multiplying the previous term by a constant
- Letter series based on alphabetical position: differences between positions may follow squares, cubes, or prime patterns
- Two-tier/interleaved series: alternate terms follow two separate independent patterns