SSC GD · Bite-size lessons

Coding and Decoding

About 7 min · General Intelligence and Reasoning · English

Time worked out from the lesson's 493 words at 150 words a minute, plus a minute for each question.

Coding and Decoding is a reasoning topic in the SSC GD syllabus that tests your ability to spot patterns and apply logical rules consistently. In these problems, a word, number, or symbol is transformed using a hidden rule, and you must decode the pattern to find the coded form of another word or the original form of a coded message.

Key ideas

• Letter Shifting — Each letter in a word moves forward or backward by a fixed number of positions in the alphabet. For example, A+2 = C, B+2 = D. Common shifts are ±1, ±2, ±3, and ±5 positions.
• Reverse Coding — The entire word or its letters are written in reverse order. Sometimes combined with letter shifting for added complexity (reverse first, then shift each letter).
• Positional Value Coding — Letters are replaced by their numeric position in the alphabet (A=1, B=2, ... Z=26) or the reverse position (A=26, B=25, etc.). These numbers may then be added, multiplied, or manipulated further.
• Mixed Alphabet Coding — Alternate letters follow different rules. For instance, letters at odd positions shift forward by 2, while letters at even positions shift backward by 1.
• Number and Symbol Substitution — Each letter is assigned a specific digit or symbol according to a key provided or implied. You apply the same key to decode or encode the target word.

Watch out for

• Confusing forward and backward shifts — Students often add when they should subtract, or vice versa. Always write the direction clearly: "R+2 = T" or "R−2 = P." Double-check the first letter's shift to set the correct direction.
• Forgetting to wrap around the alphabet — When shifting Z forward or A backward, students forget to loop. If Z+2, it wraps to B (26+2 = 28 → 28−26 = 2 = B). Always apply modulo 26 logic.
• Applying the rule to only part of the word — In mixed coding, some letters follow one rule and others a different rule. Students apply a single rule uniformly and get wrong answers. Always verify each position independently when patterns look irregular.

Quick reference

• A=1, Z=26 | Reverse: A=26, Z=1 — Memorize these for instant positional coding.
• Try small shifts first — If unsure, test ±1, ±2, ±3 first.
• Decode the first letter fast — Eliminate wrong options before solving the full word.
• Reverse + Shift often combined — If simple shift doesn't work, try reversing the word first, then apply shift.
• Check two examples minimum — One example can mislead; always confirm the rule with a second word if given.

Check yourself: 3 questions

This lesson is cut from the topic's note, not rewritten. Fact-checked on 18 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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