Coding–Decoding
Coding-decoding rewards one piece of preparation above all: knowing the alphabet positions cold. Once A=1 through Z=26 is automatic, most questions collapse into simple addition, and the rest are reversal or substitution patterns you can spot in seconds.
Updated 19 September 2026 · Reliable 2-3 questions; the letter-shift pattern dominates.
How to think about coding–decoding
Learn the alphabet positions both ways
A=1 … Z=26 forwards, and the reverse pairing A↔Z, B↔Y, C↔X (each pair sums to 27). Anchor on the milestones: E=5, J=10, O=15, T=20, Y=25. Almost every letter-based question needs one of these two mappings.
Check the shift on the first letter, then confirm on a second
Compare the first letter of the code to the first letter of the word. Whatever the gap is, verify it against another letter before committing. Many questions use a varying shift (+1, +2, +3 …) specifically to punish people who check only once.
The main pattern families
Letter shift (each letter moves a fixed or increasing number of places), reversal (the word is written backwards, sometimes then shifted), substitution (a whole word stands for another word), and number coding (letters map to digits, often by position or by a sum). Identify the family first — it decides the method.
Formulas and shortcuts
- Forward position
A=1, B=2, C=3 … Z=26 - Reverse position (opposite letter)
Opposite of a letter at position n is at position 27 − nA↔Z, B↔Y, C↔X, M↔N. Each pair sums to 27.
- Milestones worth memorising
E=5, J=10, O=15, T=20, Y=25 - Forward shift by k
New position = (old position + k), wrapping after Z
Solved examples
Q1. If CAT is coded as DBU, how is DOG coded?
- Compare letter by letter: C→D is +1, A→B is +1, T→U is +1.
- The shift is a constant +1, confirmed on all three letters.
- Apply it to DOG: D→E, O→P, G→H
Answer: EPH
Q2. If RAT is coded as 39, what is the logic and how would CAT be coded?
- Try the sum of alphabet positions: R=18, A=1, T=20.
- 18 + 1 + 20 = 39 — the code is the sum of the positions.
- Apply to CAT: C=3, A=1, T=20
- 3 + 1 + 20 = 24
Answer: CAT is coded as 24
Always test your rule against the example given before applying it — a different rule that also produced 39 would give a different answer for CAT.
Q3. If MOUSE is coded as ESUOM, how is TABLE coded?
- Compare the two: M-O-U-S-E against E-S-U-O-M.
- The code is the same letters in reverse order — no shift at all.
- Reverse TABLE: T-A-B-L-E → E-L-B-A-T
Answer: ELBAT
Practice questions with answers
1. If BOOK is coded as CPPL, then WORD is coded as:
Answer: A. XPSE — Each letter shifts +1: W→X, O→P, R→S, D→E, giving XPSE.
2. If FRIEND is coded as GSJFOE, then CANDLE is coded as:
Answer: A. DBOEMF — A +1 shift on each letter: C→D, A→B, N→O, D→E, L→M, E→F → DBOEMF.
3. If in a code LIGHT is written as GILTH, the pattern is:
Answer: B. First three letters reversed, last two swapped — LIG → GIL is that block reversed, and HT → TH is the last pair swapped. No shifting occurs.
4. If A=1 and Z=26, the sum of the letters in the word SUN is:
Answer: B. 54 — S=19, U=21, N=14. 19 + 21 + 14 = 54.
5. The letter opposite to H in the alphabet (A↔Z pairing) is:
Answer: B. S — H is at position 8. Its opposite is at 27 − 8 = 19, which is S.
6. If TEACHER is coded as VGCEJGT, the shift applied is:
Answer: B. +2 — T→V, E→G, A→C are each two places forward, so the shift is +2.
Where marks get lost
- Confirming the shift on only the first letter when the shift actually increases along the word.
- Forgetting to wrap around from Z back to A.
- Not testing a guessed rule against the example the question supplied.
- Confusing forward position with reverse position under time pressure.
Reading is not practising.
Run a timed set on coding–decoding and see which step you actually lose time on. Free, no card needed.
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