Reasoning

Coding-Decoding Guide & Practice

Learn letter coding, substitution coding, opposite letter logic, and positional value tricks with examples and free mock tests. Explore dynamic solver blueprints, master fundamental equations, examine step-by-step solved examples, and practice with real exam-grade mock test sets.

Featured in:SSC CGLSSC CHSLIBPS POIBPS ClerkRRB NTPCRRB Group D

Practice Question Papers

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Coding Decoding - Set 4 Practice Test

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25 Qs
37 min
Easy
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Coding Decoding - Set 3 Practice Test

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37 min
Easy
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Coding Decoding - Set 2 Practice Test

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25 Qs
37 min
Easy
Reasoning

Coding Decoding Practice Test

Jun 2026No attempts yet
25 Qs
25 min
Medium
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Video Tutorial

Coding-Decoding Short Tricks & Formulas

Watch this short trick video explaining high-speed shortcuts, mental math formulas, and patterns for Coding-Decoding. Master the theory and start practicing with the tests below.

Foundation & Concepts

Coding is the process of encrypting a word, letter, or sentence based on a specific set of rules or patterns. Decoding is the reverse process of deciphering the code to find the original meaning.

1. Alphabetical Positioning

To solve coding-decoding questions, it is essential to remember the positions of letters in the English alphabet:

  • Forward Order: A=1, B=2, ..., Z=26.
  • Backward Order: Z=1, Y=2, ..., A=26.

Helpful Tools:

  • EJOTY: (Forward: 5, 10, 15, 20, 25)
    • E=5, J=10, O=15, T=20, Y=25.
  • CFILORUX: (Forward: 3, 6, 9, 12, 15, 18, 21, 24)
  • Backward Order Calculation: Backward Position = 27 - Forward Position.

2. Circular Arrangement

Think of the alphabet as a circle. One step forward from Z is A; one step backward from A is Z. This is crucial for shift-based coding.

Patterns/Rules

  1. Letter-to-Letter Coding: Letters are shifted (e.g., +2, -3) or interchanged based on position.
  2. Letter-to-Number Coding: Numerical values are assigned based on positional value, sum of values, or arbitrary mapping.
  3. Substitutional Coding: Words are replaced by other words (e.g., "Blue is called Red").
  4. Chinese/Sentence Coding: Deciphering common words across multiple coded sentences to find individual codes.
  5. Conditional Coding: Codes are assigned based on specific conditions (e.g., "If first letter is a vowel and last is a consonant...").
  6. Binary/Clock Coding: Numbers or time units are converted into symbols or binary digits (0 and 1).

Typical Exam Weightage

ExamTypical Questions
SSC (CGL / CHSL / MTS)1–2 questions
Banking (IBPS / SBI)2–3 questions
Railways (RRB)1–2 questions

Modern papers favor letter-shifting and coding-by-analogy patterns over the older single-letter substitution style — practice both.

Figures are typical ranges based on recent-year patterns, not a guarantee for any specific upcoming paper — always cross-check against the latest official syllabus and previous-year papers for Coding-Decoding.

Solved Examples

1Solved Example
Easy

Q1. In a certain code, MADRAS is written as NBESBT. How is BOMBAY written in that code?

View Detailed Solution & Explanation
Step-by-Step Explanation

Each letter is shifted +1.

  • M (+1) -> N
  • A (+1) -> B
  • D (+1) -> E
  • R (+1) -> S
  • A (+1) -> B
  • S (+1) -> T
  • Answer: CPNCBZ

Q2. If "eye" is called "hand", "hand" is called "mouth", "mouth" is called "ear", "ear" is called "nose", and "nose" is called "tongue", with which of the following would a person hear?

  • Solution: A person hears with their "ear". According to the code, "ear" is called "nose".
  • Answer: Nose
2Solved Example
Moderate

Q3. If GOODNESS is coded as HNPCODTR, how is GREATNESS written?

View Detailed Solution & Explanation
Step-by-Step Explanation

Alternating shifts: +1, -1, +1, -1...

  • G (+1) -> H
  • O (-1) -> N
  • O (+1) -> P
  • D (-1) -> C
  • N (+1) -> O
  • E (-1) -> D
  • S (+1) -> T
  • S (-1) -> R
  • Applying to GREATNESS: G+1=H, R-1=Q, E+1=F, A-1=Z, T+1=U, N-1=M, E+1=F, S-1=R, S+1=T.
  • Answer: HQFZUMFRT

Q4. If WORK is coded as 4-12-9-16, how will you code WOMAN?

  • Solution: Uses backward/reverse positional values (27 - forward position).
    • W (23) -> 27-23 = 4
    • O (15) -> 27-15 = 12
    • R (18) -> 27-18 = 9
    • K (11) -> 27-11 = 16
  • Applying to WOMAN: W=4, O=12, M=14, A=26, N=13.
  • Answer: 4-12-14-26-13
3Solved Example
Hard

Q5. In a certain code language, COMPUTER is written as RFUVQNPC. How will MEDICINE be written?

View Detailed Solution & Explanation
Step-by-Step Explanation
  1. Reverse the word: RETUPMOC.
  2. The first and last letters remain same (R and C).
  3. The middle letters are shifted +1: E->F, T->U, U->V, P->Q, M->N, O->P.
  4. Result: RFUVQNPC.
  • Applying to MEDICINE:
    1. Reverse: ENICIDEM.
    2. Keep E and M: E _ _ _ _ _ _ M.
    3. Shift middle letters +1: N->O, I->J, C->D, I->J, D->E, E->F.
  • Answer: EOJDEJFM

Q6. Conditional Coding:

  • Letters: P N A J I R E B U K
  • Codes: 5 3 9 1 4 6 2 7 0 8
  • Condition: If both first and last letters are vowels, code both as $. If both are consonants, code both as #.
  • Question: Code 'KUNAJB'
  • Solution: K and B are both consonants. Rule 2 applies.
    • K -> #, U -> 0, N -> 3, A -> 9, J -> 1, B -> #.
  • Answer: #0391#