🧩 Introduction to Coding & Decoding
What is Coding & Decoding?
- Definition: A method where letters in a word are replaced by other letters based on specific rules
- Purpose: Tests logical reasoning and pattern recognition skills
- Types: Alphabet coding, number coding, symbol coding, substitution coding
- Skills Required: Observation, logical thinking, pattern identification
- Common in: Competitive exams, IQ tests, aptitude tests
- Approach: Identify the pattern/rule and apply consistently
💡 Key Insight: The same rule applies consistently throughout the entire code. Look for patterns in letter positions, shifts, or groupings!
🔤 Type 1: Coding (Forming Code)
Forward Letter Shifting
Rule: Each letter moves 2 positions forward in alphabet
- Pattern: T→V (+2), E→G (+2), A→C (+2), etc.
- Check: V comes 2 after T, G comes 2 after E
- Apply: CHILDREN = EJKNFGTO
Mixed Patterns
Rule: Alternating backward/forward shifts: -2, +2, -2, +2, -2
🔍 Type 2: Decoding (Finding Word)
Reverse Engineering
Rule: Code letters are 5 positions ahead of original
- Given: ROAD = WTFI (R→W:+5, O→T:+5, etc.)
- Find: Word for GJFY (reverse the pattern)
- Solution: GJFY = BEAT (G-5→B, J-5→E, etc.)
🔠 Type 3: Direct Letter Coding
Fixed Letter Mapping
| Letter | Code | Letter | Code |
|---|---|---|---|
| F | Q | I | H |
| R | O | E | E |
| M | Z | O | M |
| V | W | S | F |
Example: FIRE → QHOE, MOVE → ZMWE, so OVER → MWEO
🔢 Type 4: Number & Symbol Coding
Alphabet Position Coding
Rule: Replace each letter with its alphabet position
Z=26, E=5, B=2, R=18, A=1 → ZEBRA = 2652181
COBRA = C(3)O(15)B(2)R(18)A(1) = 3152181
Mathematical Operations
Rule: Sum of alphabet positions
A(1) + T(20) = 21, but given 20 (check pattern)
B(2) + A(1) + T(20) = 23, but given 40
Actual Rule: Sum × 2 = Code
CAT = C(3) + A(1) + T(20) = 24 × 2 = 48
🔄 Type 5: Substitution Coding
Word Substitution Chain
Given: ‘diamond’ → ‘gold’, ‘gold’ → ‘silver’, ‘silver’ → ‘ruby’, ‘ruby’ → ’emerald’
Question: Which is the cheapest jewel?
Logic: We know silver is cheapest, but silver is called ruby
Answer: Ruby
- Follow the substitution chain carefully
- Real-world knowledge helps but isn’t always needed
- Track what each term ACTUALLY represents in the code
🚀 Mastery Strategies
Identify Pattern Type
First determine if it’s forward/backward shift, fixed mapping, number coding, or substitution. Look for consistent differences between letters.
Create Alphabet Reference
Write A=1 to Z=26. For number coding, calculate quickly. For letter shifts, visualize the alphabet circle.
Test on Multiple Examples
If given one example, test your rule on multiple positions. If inconsistent, reconsider your pattern.
Watch for Traps
Some codes alternate patterns (odd/even positions), use reverse alphabet, or combine multiple rules.