Coding–Decoding • Topic 1 of 4

Letter Coding

In letter coding each letter moves by a fixed step. Line the plain word above the code and read the gap on the first letter; confirm it on the rest. A '+1' code turns CAT into DBU. Some codes reverse the word — always check both direction and order.

The alphabet number line

Almost every coding question is solved by writing each letter's position. Keep this strip in your head:

ABCDEFGH 12345678 +1 (C→D)
Number every letter; a "+1" shift sends C→D, A→B, T→U, so CAT becomes DBU.
Two checks every time. (1) Direction — is the shift forward (+) or backward (−)? (2) Order — is the word also reversed? Letters wrap around: Z + 1 = A, A − 1 = Z. The opposite letter of position p is 27 − p (A↔Z, B↔Y).

✅ Solved examples

1. If CAT is coded DBU, code DOG.
Each letter +1: D→E, O→P, G→H. EPH.
2. If SUN is coded RTM, code MOON.
Each letter −1: M→L, O→N, O→N, N→M. LNNM.
3. If CAT is coded TAC, code DOG.
Reverse the word: GOD.
4. If BAT is coded DCV, code COW.
Each letter +2: C→E, O→Q, W→Y. EQY.

✏️ Practice — try these, take hints as needed

1. If DOG → EPH (+1), code CAT.
+1 each.
C→D, A→B, T→U.
—
DBU
2. If FAN → HCP (+2), code RED.
+2 each.
R→T, E→G, D→F.
—
TGF
3. If KING → GNIK, code WORD.
Reverse.
—
—
DROW
4. If SUN → TVO (+1), code MAP.
+1 each.
—
—
NBQ
5. If BIG → AHF (−1), code SUN.
−1 each.
S→R, U→T, N→M.
—
RTM

📝 Topic test — 8 questions

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