Coding-Decoding
Coding-Decoding questions involve converting words, numbers, or letters into a particular code or symbolic form based on a hidden rule. The task is to decode the logic and either apply it to new words/numbers or reverse the process to find the original.
These questions test logical thinking, pattern recognition, and the ability to spot relationships in symbols or sequences.
Types of Coding-Decoding Problems
| Type | Description | Example |
|---|---|---|
| Letter Coding | Letters of a word are replaced by other letters according to a rule. | “CAT” → “DBU” (each letter shifted +1). |
| Number Coding | Words are replaced with numbers based on position, frequency, or arithmetic. | “DOG” → 4 15 7 (alphabet positions). |
| Substitution Coding | Words are replaced with entirely different words. | If “blue” means “red” and “red” means “green,” then what does “blue sky” mean? |
| Mixed Letter-Number Coding | Words coded with a mix of letters and numbers. | “SUN” → “TVO21” (letters shifted +1, position value added). |
| Symbol Coding | Symbols replace letters or words according to a pattern. | “APPLE” → “@##$%”. |
| Conditional/Mathematical Coding | Numbers or letters are coded using arithmetic or logical operations. | If A=1, B=2, then “CAB” = 3+1+2 = 6. |
How to Solve Coding-Decoding Questions
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Compare coded and original form: Identify the exact transformation.
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Check for consistency: The same rule applies across all letters/numbers.
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Look for common rules:
- Alphabet positions (A=1, B=2, …).
- Shifting (+1, −1, reverse order).
- Mathematical patterns with numbers.
- Direct substitution.
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Apply the rule: Use it to encode/decode new words.
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Verify with options: In exams, eliminate options that break the rule.
Conceptual Tips and Common Mistakes
- Alphabet position mastery: Knowing A=1, M=13, Z=26 helps quickly.
- Check for direction: Shifts may be forward (+) or backward (−).
- Don’t assume same rule always: Sometimes words use reverse alphabets, sometimes arithmetic.
- Be cautious with substitution: “Blue = Red” means in the puzzle’s language, not actual meaning.
- Practice speed: Coding-decoding often requires quick identification.
Examples
Example 1 — Letter Coding
Word: “BALL”
Code: “CBMM”
Rule: Each letter shifted +1 → B→C, A→B, L→M, L→M.
Answer: “BALL” → “CBMM”.
Example 2 — Number Coding
Word: “DOG”
Rule: Replace letters with positions → D=4, O=15, G=7.
Answer: “DOG” → 4 15 7.
Example 3 — Substitution Coding
If “sky” = “water,” “water” = “blue,” “blue” = “cloud,” then what is the color of “sky”?
Answer: Water = Blue → Sky = Water → Sky = Blue.
Example 4 — Reverse Alphabet Coding
Word: “CAT”
Rule: Replace each letter with its reverse alphabet position (A↔Z, B↔Y, C↔X).
C→X, A→Z, T→G.
Answer: “CAT” → “XZG”.