Coding-Decoding Cheat Sheet
2 Nov 2026
Quick answer
A quick reasoning revision sheet for coding-decoding — letter-position values, letter-shift coding, number and symbol coding, and substitution (fictitious-language) coding — with the step-by-step method for finding the rule and a worked example, for fast SSC, Banking and Railway revision.
In coding-decoding, a word or message is written by a hidden rule, and you must find the rule from a given example and apply it. The whole skill is spotting the pattern.
The letter-position values
Most coding rests on each letter's position in the alphabet. Memorise them, forwards and backwards.
A=1 B=2 C=3 D=4 E=5 F=6 G=7 H=8 I=9 J=10 K=11 L=12 M=13 N=14 O=15 P=16 Q=17 R=18 S=19 T=20 U=21 V=22 W=23 X=24 Y=25 Z=26
The EJOTY trick fixes the fifth letters: E=5, J=10, O=15, T=20, Y=25. The reverse position of any letter is 27 − its position (A↔Z, B↔Y, …).
The common types
| Type | How it works | Example |
|---|---|---|
| Letter shift | each letter moves forward/back by a fixed number | CAT → DBU (+1 each) |
| Reverse | letter replaced by its opposite (27 − position) | ACE → ZXV |
| Number coding | each letter replaced by its position or a formula | ACE → 1, 3, 5 |
| Symbol coding | letters/words map to symbols in a given key | apply the key as given |
| Substitution | whole words stand for other words (a "language") | "sky is blue" rules |
The method
- Line the code up against the original, letter by letter.
- Find the gap (position difference) or the rule that turns each letter into its code.
- Check the rule works for every letter, not just the first.
- Apply the same rule to the new word.
Worked example
If CAT is coded as DBU, how is DOG coded?
- C→D (+1), A→B (+1), T→U (+1): the rule is +1 to each letter.
- Apply to DOG: D→E, O→P, G→H.
- Answer: EPH.
Quick tips
- Always test the rule on the last letter too — many questions hide a change in the pattern partway.
- For substitution-language questions, make a small table of word → meaning before answering.
Revise the full method in the Coding-Decoding lesson, then practise coding-decoding questions or browse more reasoning revision sheets.
How this was made: Drafted with AI assistance; every formula and worked figure recomputed independently; every fact checked against the source it cites.