Coding Decoding

Table of Contents

1. 1: Foundation & Types of Coding
2. 2: Letter / Alphabet Coding
3. 3: Number / Symbol Coding
4. 4: Substitution / Conditional Coding
5. 5: Advanced Puzzles & Data Sufficiency

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1: Foundation & Types of Coding

1.1 What is Coding?

Coding is a process where a given word, number, or set of characters is transformed into another form according to a specific rule. The rule may involve:

· Positional shifts (e.g., each letter moved forward/backward by a fixed number)
· Reversal (e.g., writing the word backwards)
· Mathematical operations (e.g., adding or subtracting numbers, squaring digits)
· Substitution (e.g., each letter replaced by another based on a key)
· Symbolic mapping (e.g., @ for A, # for B, etc.)

In exams, you are usually given one or more examples of coding (e.g., “MANGO” is coded as “NBOHP”) and you must find the code for another word, or decode a given code back to the original.

1.2 Types of Coding

• Type 1 – Letter Based Coding: Only letters are involved. Transformations include fixed shifts, reverse order, skipping patterns, etc.
• Type 2 – Number Based Coding: Numbers are coded into other numbers or letters (e.g., 1=A, 2=B).
• Type 3 – Symbol Based Coding: Symbols (@, #, $, %, etc.) are used as codes for characters.
• Type 4 – Mixed Coding: Combines letters, numbers, and symbols.
• Type 5 – Substitution / Conditional Coding: A word/phrase is replaced by another based on a rule (e.g., “apple” means “orange”).
• Type 6 – Advanced / Multi‑step Coding: Multiple operations applied in sequence (e.g., reverse then shift).

1.3 General Methodology

1. Observe the example(s): Identify the relationship between original and coded terms.
2. Formulate a rule: Determine the specific transformation.
3. Test the rule: Ensure it works consistently across all given examples.
4. Apply/Decode: Apply to the target term or reverse for decoding.
5. Consider patterns: Shifts, reversal, opposites, sums, etc.

1.4 Common Patterns in Coding

1.5 Worked Examples – Foundation Level

Example 1 – Simple Shift

Question: If “MANGO” is coded as “NBOHP”, how is “APPLE” coded?

• Step 1: Compare letters: M+1=N, A+1=B, N+1=O, G+1=H, O+1=P. Rule: +1 shift.
• Step 2: Apply to APPLE: A+1=B, P+1=Q, P+1=Q, L+1=M, E+1=F.
• Answer: BQQMF

Example 2 – Reverse Order

Question: If “PLANE” is coded as “ENALP”, how is “CLOUD” coded?

• Step 1: Code is reverse of original.
• Step 2: Reverse “CLOUD” → “DUOLC”.
• Answer: DUOLC

Example 3 – Opposite Letters

Question: If “LION” is coded as “ORLM”, find the code for “TIGER”.

• Step 1: Check mapping: L(12)→O(15) [27-12=15], I(9)→R(18) [27-9=18]. Rule: Opposite letters.
• Step 2: Apply to TIGER: T→G, I→R, G→T, E→V, R→I.
• Answer: GRTVI

1.6 Common Mistakes & How to Avoid Them

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2: Letter / Alphabet Coding

2.1 Core Concepts – Alphabet Positions

Instant mapping is key:

• Forward: A=1, B=2, ..., Z=26
• Reverse: Z=1, Y=2, ..., A=26 (Mapping: 27 - Forward Position)
• EJOTY: E=5, J=10, O=15, T=20, Y=25 (Reference anchors)

2.2 Types of Letter Coding

• Fixed Shift: Constant offset applied to every letter.
• Reverse Order: Word is simply mirrored.
• Opposite Letters: A replaced by Z, B by Y, etc.
• Increasing/Skipping Shifts: Pattern like +1, +2, +3 or +2, +2, +2.
• Vowel/Consonant Logic: Vowels and consonants follow separate shift rules.
• Mixed Operations: Sequential steps (e.g., reverse then shift).

2.3 Worked Examples

Example 1 – Fixed Forward Shift

Question: If “PENCIL” is coded as “QFODJM”, what is “ERASER”?

• Step 1: P+1=Q, E+1=F, N+1=O... Rule: +1.
• Step 2: Apply to ERASER: E+1=F, R+1=S, A+1=B, S+1=T, E+1=F, R+1=S.
• Answer: FSBTFS

Example 2 – Opposite Letters

Question: If “CHAIR” is coded as “XSZRI”, find code for “TABLE”.

• Step 1: C(3)→X(24) [3+24=27]. Rule: Opposite mapping.
• Step 2: Apply to TABLE: T→G, A→Z, B→Y, L→O, E→V.
• Answer: GZYOV

Example 3 – Mixed Operation (Reverse then Shift)

Question: If “MIND” is coded as “EOJN”, find code for “BODY”.

• Step 1: Reverse “MIND” = “DNIM”. Shift each +1: D+1=E, N+1=O, I+1=J, M+1=N.
• Step 2: Apply to BODY: Reverse = “YDOB”. Shift each +1: Y+1=Z, D+1=E, O+1=P, B+1=C.
• Answer: ZEPC

2.4 Practice Set – Letter Coding

1. If “TABLE” is coded as “UBCMF”, code “CHAIR”.
   • Answer: DIBJS (+1 each).
2. If “CLOUD” is coded as “XOLFW” (opposite letters), code “STORM”.
   • Answer: HGLIN (Opposite mapping).
3. If “DELHI” is coded as “FGNJK”, code “MUMBAI”.
   • Answer: OWODCK (+2 each).
4. If “TRAIN” is coded as “NIART”, code “STATION”.
   • Answer: NOITATS (Reversed).
5. If “ZEBRA” is coded as “AFCSB”, code “YACHT”.
   • Answer: ZBDIU (+1 each, with wrap-around Z→A).

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Summary of Subtopic 2

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3: Number / Symbol Coding

3.1 Core Concepts – Numbers and Symbols in Coding

Number / symbol coding can take several forms:

• Number‑to‑Letter coding: Numbers represent positions in the alphabet (e.g., 1 = A, 2 = B, …).
• Number‑to‑Number coding: Operations on digits (e.g., reverse, sum of digits, product, square, etc.).
• Symbol‑to‑Letter / Number: Symbols act as substitutes for letters or numbers (e.g., @ = A, # = B, etc.).
• Symbol sequences: Symbols following a specific progression (e.g., @, #, $, %, …).

3.2 Common Types

• Type 1 – Position Mapping: Numbers correspond to alphabet positions (1=A, 2=B).
• Type 2 – Digit Manipulation: Operations like reversing digits (123 → 321), sum of digits (23 → 5), or product (23 → 6).
• Type 3 – Arithmetic Operations: Numbers transformed via a formula (e.g., n → 2n + 1).
• Type 4 – Symbol Sequences: Symbols follow a keyboard or predefined order.
• Type 5 – Mixed Components: Letter, Number, and Symbol each follow separate rules (e.g., “A1@” → “B2#”).
• Type 6 – Direct Substitutes: A mapping table provides the key (e.g., @ = A, # = B).

3.3 Step‑by‑Step Approach

1. Identify the Data Type: Numbers only, symbols only, or a mixed set?
2. Analyze Numbers:
   • Values 1–26 → suspect alphabet mapping.
   • Same digit count → check reversal or digit sum.
   • Longer/Shorter code → suspect arithmetic formulas.
3. Decode Symbols:
   • Check for keyboard sequences (@, #, $, %, &).
   • Look for one-to-one alphabetical mapping.
4. Resolve Mixed Strings: Treat letters, numbers, and symbols as independent streams.
5. Verify across Examples: Ensure the rule holds for all given samples.

3.4 Worked Examples

Example 1 – Position Mapping

Question: If 1, 3, 5, 12, 15 is coded as A, C, E, L, O, then code 2, 9, 14, 20, 5.

• Step 1: Rule: number = letter position.
• Step 2: 2=B, 9=I, 14=N, 20=T, 5=E.
• Answer: BINTE

Example 2 – Digit Manipulation (Sum)

Question: If 23 is coded as 5, 45 as 9, then what is the code for 89?

• Step 1: Rule: sum of digits (2+3=5, 4+5=9).
• Step 2: 8+9=17.
• Answer: 17

Example 3 – Mixed (Symbol + Number)

Question: If “@1” is coded as “#2”, code “%4”.

• Step 1: Symbol +1 in sequence (@→#), number +1.
• Step 2: % → &, 4+1=5.
• Answer: &5

Example 4 – Arithmetic Formula

Question: If 3 is coded as 7, 5 as 11, code 8.

• Step 1: Rule: 2n + 1 (3×2+1=7; 5×2+1=11).
• Step 2: 8×2+1 = 17.
• Answer: 17

3.5 Common Mistakes & How to Avoid Them

3.6 Pro Tips

• 1-26 Range: Always check for A=1 mapping first.
• Keyboard Logic: Familiarize yourself with the symbol order on a standard QWERTY keyboard.
• Substitution Tables: For complex puzzles, draw a small reference table to keep mapping consistent.
• Mixed Consistency: If first letter +1, all letters likely +1.

3.7 Practice Set – Number / Symbol Coding

1. Number → Letter: If 9, 21, 14, 7 is coded as I, U, N, G, code 20, 5, 19, 20.
   • Answer: TEST
2. Digit Sum: If 12 → 3, 34 → 7, code 78.
   • Answer: 15
3. Digit Product: If 23 → 6, 34 → 12, code 45.
   • Answer: 20
4. Symbol Sequence: If @ → #, # → $, code %.
   • Answer: &
5. Mixed: If “A2” → “B3”, code “E6”.
   • Answer: F7
6. Arithmetic: If 2 → 5, 3 → 7, code 4.
   • Answer: 9 (2n + 1).

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Summary of Subtopic 3

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4: Substitution / Conditional Coding

4.1 Core Concepts – Substitution & Conditional Coding

• Substitution Coding: Words or letters are replaced by other words/letters based on a fixed mapping (e.g., “mango” → “apple”).
• Conditional Coding: Transformation rules depend on specific properties like character type (vowel/consonant), position (odd/even), or word length.

4.2 Types of Substitution / Conditional Coding

• Word Substitution (Chain): Each word is called by another name (e.g., “red” is “blue”).
• Letter Transformations: Based on category (e.g., vowel → next vowel).
• Position-Based: Rules vary by index (e.g., 1st letter +1, last letter -1).
• Global Conditions: Rules apply to the whole word (e.g., “if word length is even, reverse it”).
• Language Puzzles: Comparing multiple coded sentences to deduce specific word-to-word mappings.

4.3 Step‑by‑Step Approach

For Word Substitution:

1. Map the given chain (Word A → Word B).
2. Directly replace the target word with its assigned "called" name.

For Conditional Logic:

1. Categorize characters (vowel, consonant, odd/even position).
2. Apply the specific rule to each category.
3. Handle wrap-around or special cases (e.g., Z+1 = A).

4.4 Worked Examples

Example 1 – Word Substitution (Chain)

Question: If “apple” is called “mango”, “mango” is called “banana”, what is “apple” called?

• Step 1: Look at the direct mapping: “apple” → “mango”.
• Answer: mango

Example 2 – Conditional Coding (Odd/Even Position)

Question: If odd letters shift forward by 1 and even letters shift backward by 1, code “BEAUTY”.

• Step 1: 1:B(+1)=C, 2:E(-1)=D, 3:A(+1)=B, 4:U(-1)=T, 5:T(+1)=U, 6:Y(-1)=X.
• Answer: CDBTUX

Example 3 – Word Substitution (Cipher Puzzle)

Question:

• “I am good” = “A B C”
• “You are good” = “D B C”
• Find code for “I”.
• Step 1: Compare sentences. “good” is in both (code C). “B” is also in both (likely “am/are”).
• Step 2: “I” is the first word in the first sentence. Code = A.
• Answer: A

4.5 Common Mistakes & How to Avoid Them

4.6 Pro Tips

• Mapping Tables: Draw out word relationships for chain puzzles.
• Sentence Comparison: In language puzzles, identify common words and their overlapping codes first.
• Systematic Application: For complex rules, handle one condition at a time (e.g., do all vowels first, then all consonants).

4.7 Practice Set – Substitution / Conditional Coding

1. Word Chain: If “Sky” is “Star”, “Star” is “Cloud”, “Cloud” is “Earth”, where does it rain from?
   • Answer: Earth (Rain comes from Cloud, Cloud is called Earth).
2. Conditional (Vowel/Consonant): If Vowel → Next Vowel and Consonant → Next Consonant, code “CAKE”.
   • Answer: DULA (C→D, A→E? Wait, rule: A→E, K→L, E→I → DELI? Let's check mapping: C→D, A→E, K→L, E→I → DELI).
3. Language Puzzle: If “Go Home” = “Ka Pa” and “Come Home” = “Sa Pa”, find code for “Home”.
   • Answer: Pa (Common word in both).
4. Position Based: If first letter +1 and last letter -1, code “MIND”.
   • Answer: NINC.
5. Logic Based: If word starts with Vowel, reverse it. If Consonant, shift +1. Code “EAT” and “BAT”.
   • Answer: TAE and CBU.

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Summary of Subtopic 4

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5: Advanced Puzzles & Data Sufficiency

5.1 What Are Advanced Coding Puzzles?

Advanced coding puzzles go beyond a single transformation. They may involve:

• Multi‑step Coding: Two or more operations applied in sequence (e.g., reverse then shift).
• Condition-Based logic: The rule changes based on word properties (e.g., if word length is even, apply different rules).
• Puzzle-Based reasoning: Deducing codes from partial relational information.
• Data Sufficiency (DS): Evaluation of given statements to determine if a unique code can be derived.

5.2 Types of Advanced Puzzles

• Type 1 – Multi‑step Coding: Sequential transformations (e.g., Step 1: Reverse, Step 2: Shift +1).
• Type 2 – Conditional / Mixed Operations: Branching logic based on word length or character composition.
• Type 3 – Puzzle‑Based Coding: Deducing patterns through elimination across multiple comparative examples.
• Type 4 – Data Sufficiency: Deciding if given information is enough to solve a specific coding question uniquely.

5.3 Step‑by‑Step Approach for Advanced Puzzles

1. Parse the Pipeline: Identify all operations and their strict order.
2. Execute Sequentially: Apply transformations one by one; verify intermediate results.
3. Evaluate Conditions first: For branching rules, first check word properties (vowel count, length, etc.).
4. Solve for Uniqueness: In Data Sufficiency, ensure the statement allows for only one possible answer.
5. Cross-Verify: Test your deduced rule on all provided samples to ensure total consistency.

5.4 Worked Examples

Example 1 – Multi‑step Coding

Question: In a code: (1) Reverse the word; (2) Shift vowels forward by 1 (A→E, E→I...); (3) Shift consonants +2. Code “GAME”.

• Step 1: Reverse “GAME” → “EMAG”.
• Step 2: Vowels: E→I, A→E → “IMEG”.
• Step 3: Consonants: M+2=O, G+2=I. Result = I O E I.
• Answer: IOEI

Example 2 – Data Sufficiency

Question: What is the code for “PARK”?

• Statement I: “CORE” is coded as “DPSF”.
• Statement II: “BALL” is coded as “CBMM”.
• Analysis: Both statements suggest a +1 shift independently.
• Answer: Each alone is sufficient.

Example 3 – Conditional (Word Length)

Question: If word length is even, reverse it; if odd, shift backward -1. Code “BOTTLE” and “PEN”.

• Step 1: “BOTTLE” (6 letters, even) → reverse → “ELTTOB”.
• Step 2: “PEN” (3 letters, odd) → shift -1: P→O, E→D, N→M.
• Answer: ELTTOB, ODM

5.5 Common Mistakes & How to Avoid Them

5.6 Pro Tips

• Intermediate Snapshots: In multi-step coding, write down the word after each operation.
• DS Strategy: Check Statement I → Check Statement II → Check I+II only if independent checks fail.
• Pattern Matching: In advanced puzzles, look for fixed letter placements first (e.g., middle letter never changes).

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Summary of Subtopic 5

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Complete Coding Decoding – Final Recap

We have successfully covered the full spectrum of Reasoning Coding:

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Official Coding Decoding Practice Lab (50 MCQs)