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Coding-Decoding

About 6 min · Logical Reasoning · English

Time worked out from the lesson's 425 words at 150 words a minute, plus a minute for each question.

Coding-Decoding is a pattern-recognition topic in logical reasoning where words, letters or numbers are transformed using a specific rule. Your task is to identify the rule from examples and then apply it to encode a new word or decode a given code. This topic is a quick-scoring section if you master the common patterns.

Key ideas

• Letter Position Value: Each letter has a position in the alphabet—A=1, B=2, C=3, ... Z=26. Many codes involve adding or subtracting from these positions.
• Reverse Alphabet: The reverse alphabet maps A↔Z, B↔Y, C↔X, etc. A common trick is to replace each letter with its opposite-end partner.
• Shift/Caesar Cipher: Move every letter forward or backward by a fixed number of steps (e.g. shift +3 means A→D, B→E, C→F).
• Arithmetic Operations on Positions: Add, subtract, multiply or divide the position values and convert the result back to a letter (e.g. if position value exceeds 26, apply modulo 26 or wrap around).
• Symbol or Number Substitution: Letters are replaced by symbols or numbers according to a given key, or each letter is assigned a fixed digit.

Watch out for

• Confusing forward and backward shifts: If the code shifts letters backward, students often shift forward by mistake. Always test your rule on all letters in the example before applying it. Fix: Write down position values explicitly.
• Forgetting to wrap around past Z: When shifting forward beyond Z (e.g. Y+3), students forget to wrap to B (Y=25, +3=28, 28−26=2=B). Fix: Use modulo 26 arithmetic or subtract 26 when result >26.
• Mixing up reverse alphabet: Students remember A↔Z but miscalculate middle letters (e.g. M↔N is 13↔14, correct reverse of M is N by 27−13=14, which is N, but true opposite of M is N only if you mean reverse order; actually M=13 reverse is 27−13=14=N, so M↔N is correct reverse pair).

Quick reference

• A=1, Z=26 — memorize letter positions for the first 10 and last 5 letters.
• Reverse alphabet formula: position of reverse = 27 − original position.
• Common shift: +3 (Caesar cipher) or +1 (next letter).
• Check vowels vs consonants — many problems treat them differently.
• Answer choice testing — if stuck, plug answer choices backward into the rule.

Check yourself: 3 questions

This lesson is cut from the topic's note, not rewritten. Fact-checked on 21 Oct 2026: an AI-assisted check of this note against cited sources; the errors it found were corrected that day. Some errors may remain. The questions are from Shishya's validated question bank.

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