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Coding and Decoding

Practice MCQs

Coding and Decoding questions test your ability to identify a hidden rule and apply the same rule to a new word, number, or message.

Reasoning Ability Coding and Decoding Competitive Exams

Coding and Decoding is an important reasoning ability topic where words, letters, numbers, or symbols are written in a coded form. Your task is to identify the hidden rule and decode the correct answer.

What is Coding and Decoding?

Coding means converting a word, number, or message into another form using a particular rule. Decoding means identifying the rule and converting the coded message back into its original or required form.

In competitive exams, coding and decoding questions may use alphabet positions, reverse alphabet order, letter shifting, number values, symbols, word substitution, or mixed patterns. The key is to find the rule used in the given example and apply the same rule to the question.

Quick idea: Compare the original word and coded word letter by letter. Check whether letters are shifted forward, shifted backward, reversed, or replaced by numbers.
Original Code Rule
CAT DBU Each letter is moved one step forward.
DOG CNF Each letter is moved one step backward.
BAD 214 Letters are replaced by alphabet positions.
TOP KLM Letters are replaced by reverse alphabet positions.

“Coding and decoding questions are solved by finding the hidden rule, not by guessing the code.”

Reasoning Tip
Key points
  • Compare given word and code carefully.
  • Use alphabet position values.
  • Check forward and backward letter shifts.
  • Look for reverse alphabet coding.
  • Check whether letters are rearranged.
  • Apply the same rule to the new word.
letters numbers symbols hidden rule

Alphabet Position Chart

Alphabet positions are very important in coding and decoding questions. Many codes are formed by adding, subtracting, or reversing alphabet positions.

ABCDEFG HIJKLM
1234567 8910111213
NOPQRST UVWXYZ
14151617181920 212223242526
Memory tip: A = 1, E = 5, J = 10, O = 15, T = 20, and Z = 26. For reverse coding, A pairs with Z, B with Y, C with X, and so on.

Common Types of Coding and Decoding Questions

Coding and decoding questions may be based on letters, numbers, symbols, word replacement, or mixed logic. The following types are commonly asked in competitive exams.

Letter Shifting

Each letter is moved forward or backward.

  • CAT → DBU
  • C + 1 = D
  • A + 1 = B
  • T + 1 = U
Number Coding

Letters are replaced by numbers.

  • A = 1
  • B = 2
  • CODE = 3 15 4 5
  • Use alphabet positions
Reverse Alphabet Coding

Letters are replaced by opposite letters.

  • A ↔ Z
  • B ↔ Y
  • C ↔ X
  • CAT → XZG
Substitution Coding

Words are replaced by code words.

  • “sky is blue” → “pa la ma”
  • Compare statements
  • Find common words
  • Decode meaning
Rule: Do not assume that the code is always based on +1 or -1. Check all letters and confirm the same rule is applied throughout.
Coding Pattern Bank
Forward Shift
A → B, B → C, C → D
CAT → DBU
Each letter moves +1
Backward Shift
D → C, O → N, G → F
DOG → CNF
Each letter moves -1
Position Coding
A = 1, B = 2, C = 3
BAD → 2 1 4
CODE → 3 15 4 5
Reverse Coding
A = Z, B = Y, C = X
DOG → WLT
Use opposite alphabet

Tip: Compare the first and last letters also. Many questions use shifting from both sides.

Coding and decoding reasoning concept
Coding and Decoding questions test your ability to identify a hidden rule and apply the same rule to a new word, number, or message.

Step-by-Step Solving Method

Step Action Example
Step 1 Write the original word and coded word clearly. CAT → DBU
Step 2 Compare each corresponding letter. C → D, A → B, T → U
Step 3 Find the movement or rule. Each letter moves +1.
Step 4 Check whether the rule applies to all letters. C + 1 = D, A + 1 = B, T + 1 = U.
Step 5 Apply the same rule to the new word. DOG → EPH.
Important: In mixed coding, letters may be shifted and then rearranged. Always check whether order is also changed.

Solved Examples

Question Method Answer
If CAT is coded as DBU, how is DOG coded? CAT → DBU means each letter moves +1.
D + 1 = E, O + 1 = P, G + 1 = H. 		EPH
If DOG is coded as CNF, how is CAT coded? DOG → CNF means each letter moves -1.
C - 1 = B, A - 1 = Z, T - 1 = S. 		BZS
If BAD is coded as 214, how is CAB coded? BAD → 214 means alphabet positions are used.
C = 3, A = 1, B = 2. 		312
If A is coded as Z and B is coded as Y, how is CAT coded? Use reverse alphabet coding.
C → X, A → Z, T → G. 		XZG
If ROAD is coded as URDG, how is LAMP coded? R → U, O → R, A → D, D → G.
Each letter moves +3.
L → O, A → D, M → P, P → S. 		ODPS
If MANGO is coded as NZOHP, how is APPLE coded? Each letter moves +1.
A → B, P → Q, P → Q, L → M, E → F. 		BQQMF
If DELHI is coded as CDKGH, how is PATNA coded? Each letter moves -1.
P → O, A → Z, T → S, N → M, A → Z. 		OZSMZ
If BOOK is coded as 2151511, how is PEN coded? Use alphabet positions.
B = 2, O = 15, O = 15, K = 11.
P = 16, E = 5, N = 14. 		16514

Note: In number coding, single-digit and double-digit alphabet positions may be written together. Read carefully before decoding.

Common Traps and Shortcuts

Common Traps
  • Assuming every code uses +1 letter movement.
  • Ignoring backward letter movement.
  • Forgetting reverse alphabet coding.
  • Not checking whether letters are rearranged.
  • Confusing alphabet position with term position.
  • Reading number codes incorrectly when digits are joined together.
Useful Shortcuts
  • Write alphabet positions above the letters.
  • Compare first letter with first coded letter.
  • Check whether all letters follow the same shift.
  • Use reverse pair memory: A-Z, B-Y, C-X, D-W.
  • For long words, check first, middle, and last letters.
  • Verify the final code by applying the rule again.
Exam approach: Identify whether the question is based on forward shift, backward shift, alphabet position, reverse alphabet, word substitution, or mixed coding.

Practice

A) Multiple Choice Questions
  1. If CAT is coded as DBU, how is DOG coded?
    EPH CNG FQI DOH
  2. If BAD is coded as 214, how is CAB coded?
    312 321 231 213
  3. If A is coded as Z, B as Y, then CAT is coded as:
    XZG YAG WZF XAG
  4. If ROAD is coded as URDG, how is LAMP coded?
    MBNQ ODPS KZLO NCOR
  5. If DELHI is coded as CDKGH, how is PATNA coded?
    QBUOB OZSMZ PZSMB OASNZ
B) Solve the Higher-Order Problems
  1. If MANGO is coded as NZOHP, how is APPLE coded? (Hint: Check forward letter shift.)
  2. If SCHOOL is coded as RBGNNK, how is TABLE coded? (Hint: Check backward letter shift.)
  3. If KING is coded as PRMT using reverse alphabet coding, how is QUEEN coded? (Hint: Use A-Z, B-Y, C-X reverse pairs.)
  4. If BOOK is coded as 2151511, how is PEN coded? (Hint: Use alphabet positions.)
  5. If TRAIN is coded as WUDLQ, how is BUS coded? (Hint: Check each letter shift in TRAIN.)
C) Match the Coding Type with the Correct Rule
Coding Type Correct Rule / Meaning
Forward Shift Each letter moves ahead in alphabet order
Backward Shift Each letter moves backward in alphabet order
Alphabet Position Coding Letters are replaced by their position numbers
Reverse Alphabet Coding A becomes Z, B becomes Y, C becomes X
Substitution Coding Words or symbols are replaced by fixed codes
Mixed Coding More than one rule is used together
Reasoning Reminder

Coding and decoding questions are solved by identifying the hidden rule used to transform the original word or message into code. The rule may involve alphabet movement, number position, reverse alphabet, symbol substitution, word substitution, or mixed operations.

Task: Create five coding and decoding questions using forward shift, backward shift, alphabet position, reverse alphabet, and mixed coding patterns.

Show Suggested Answers
Multiple Choice
  1. EPH
    CAT → DBU means each letter moves +1.
    D → E, O → P, G → H.
  2. 312
    BAD → 214 uses alphabet positions.
    C = 3, A = 1, B = 2.
  3. XZG
    Reverse alphabet coding: C → X, A → Z, T → G.
  4. ODPS
    ROAD → URDG means each letter moves +3.
    L → O, A → D, M → P, P → S.
  5. OZSMZ
    DELHI → CDKGH means each letter moves -1.
    P → O, A → Z, T → S, N → M, A → Z.
Higher-Order Problems
  1. MANGO → NZOHP uses +1 shift.
    APPLE → BQQMF.
    Answer = BQQMF.
  2. SCHOOL → RBGNNK uses -1 shift.
    TABLE → SZAKD.
    Answer = SZAKD.
  3. Reverse alphabet coding:
    Q → J, U → F, E → V, E → V, N → M.
    QUEEN → JFVVM.
  4. BOOK → 2151511 uses alphabet positions.
    P = 16, E = 5, N = 14.
    PEN → 16514.
  5. TRAIN → WUDLQ uses +3 shift for each letter.
    B → E, U → X, S → V.
    BUS → EXV.
Concept Matching
  1. Forward Shift → Each letter moves ahead in alphabet order
  2. Backward Shift → Each letter moves backward in alphabet order
  3. Alphabet Position Coding → Letters are replaced by their position numbers
  4. Reverse Alphabet Coding → A becomes Z, B becomes Y, C becomes X
  5. Substitution Coding → Words or symbols are replaced by fixed codes
  6. Mixed Coding → More than one rule is used together
Clue Explanation

Coding and decoding questions should be solved by comparing the original and coded forms. Once the transformation rule is identified, apply the same rule carefully to the new word.

Exam tips
  • Compare original and coded words letter by letter.
  • Check forward and backward shifts.
  • Use alphabet position chart for number codes.
  • Remember reverse pairs: A-Z, B-Y, C-X.
  • Check whether letters are rearranged.
  • Verify the rule before selecting the answer.
Practice MCQs