SSC MTS · Bite-size lessons

Coding-Decoding

About 6 min · Reasoning Ability and Problem Solving · English

Time worked out from the lesson's 396 words at 150 words a minute, plus a minute for each question.

Coding-Decoding is a fundamental reasoning topic in SSC MTS where information (letters, numbers, or words) is encrypted using a specific rule, and you must either decode the given code or encode new information using the identified pattern. This topic tests your pattern recognition ability and logical thinking under time pressure.

Key ideas

• Letter Coding: Each letter is replaced according to a fixed rule—most commonly alphabetical position shifts (forward or backward), reverse alphabet substitution, or position-based arithmetic operations.
• Number Coding: Words or letters are converted to numbers based on alphabetical positions (A=1, B=2... Z=26), then arithmetic operations (addition, multiplication, difference) are applied.
• Substitution Coding: Direct replacement where specific letters/numbers are swapped with predetermined symbols or other letters, creating a cipher-like code.
• Conditional Coding: The coding rule changes based on word characteristics like number of letters, vowel/consonant pattern, or position of specific letters within the word.
• Pattern Verification: Always test your identified rule against ALL given examples before selecting an answer—one match is coincidence, consistent matches confirm the pattern.

Watch out for

• Single Example Assumption → Testing pattern on only one word pair and assuming it's correct. Fix: Always verify against minimum two examples before answering.
• Ignoring Wrap-Around → When shifting Z forward or A backward, forgetting alphabet cycles (Z+1=A, A-1=Z). Fix: Use modulo 26 logic—if position >26, subtract 26; if <1, add 26.
• Position Calculation Errors → Miscounting alphabet positions (common errors: E as 6 instead of 5, M as 14 instead of 13). Fix: Count on fingers for unfamiliar letters or memorize positions 1–26.

Quick reference

• First step: Write down position numbers (A=1...Z=26) for all letters in the example
• Check three patterns first: simple shift (+1,+2,-1), reverse alphabet (27-n), position sum
• Reverse alphabet quick check: first letter and coded letter positions should sum to 27
• For mixed coding: separate examples by word length—may have different rules per length
• Time-saving: If answer choices differ in first letter only, decode just the first letter

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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