Coding & Decoding

Two foundations: the alphabet number line (with the EJOTY trick — E5, J10, O15, T20, Y25) and the opposite-letter formula, opposite position $= 27 - \text{position}$ (A↔Z, B↔Y, …).

Pattern Catalogue

1. Letter shift (Caesar): each letter moves a fixed number of steps (watch for a variable shift like +1, +2, +3…).
2. Opposite / mirror: every letter → its mirror via $27 - \text{position}$.
3. Number / position: letter → its alphabet number (confirm A=1 vs Z=1 from the example).
4. Matrix / coordinate: letter → (row, column); deduce row-first vs column-first from the example.
5. Symbol / number substitution: an arbitrary lookup table, no logic — map carefully.
6. Word substitution: "apple is called orange…" — build the swap table first, then re-read.
7. Sum / difference: code = sum (or product / difference) of letter positions, e.g. CAT = 3+1+20 = 24.
8. Reversed / jumbled: letters reversed, or reversed in groups.

Universal Method

1. Extract the rule from the given example only — never guess it from the target word.
2. Apply the same operation, direction and order to the new word.
3. For coded sentences, build one combined word→code dictionary from all the example sentences before answering.

Most common mistakes: assuming A=1 when the paper uses Z=1 (check with EJOTY); missing that vowels / consonants may follow different rules; transposing row and column in matrix coding.