Coding-Decoding LRDI

Coding-Decoding LRDI problems involve puzzles where words, numbers, or symbols are replaced with codes according to a hidden rule. Unlike direct verbal coding-decoding, the LRDI version is often tabular, caselet-based, or multi-rule driven, requiring cross-referencing to decode correctly.

Common Types of Coding-Decoding LRDI Problems

  1. Letter Coding

    • Words are coded by shifting letters or substituting them with others.
    • Example: CAT → DBU (each letter shifted +1).

  2. Number Coding

    • Words or letters are represented by numbers based on position, sum, or pattern.
    • Example: CAT → 3 1 20 (alphabet positions).

  3. Symbol Coding

    • Relations or words expressed using symbols.
    • Example: A @ B = A is the brother of B.

  4. Conditional Coding (Puzzle Type)

    • A table or set of rules is given. Each condition applies differently.
    • Example: If “%” means +, “#” means ×, then 3 % 5 # 2 = (3+5) × 2 = 16.

  5. Matrix/Table Coding

    • Codes arranged in a grid; locate word/number at intersections.
    • Example: Table with rows = letters, columns = digits → code for word.

How to Solve Step by Step

  1. Identify the coding rule: Check for patterns (alphabet shifts, arithmetic, symbol replacement).
  2. Test rule consistency: Apply to all examples given; rule must hold across.
  3. Build a code map/table: Useful in symbol/matrix-based sets.
  4. Decode systematically: Don’t jump to conclusions—many codes look similar.
  5. Cross-check final answer: Always verify against original clues.

Conceptual Tips and Common Mistakes

  • Don’t assume one rule fits all: Some puzzles use different rules for different cases.
  • Be careful with positions: Forward vs backward alphabet orders are common traps.
  • Mixed coding traps: Codes may mix letters, numbers, and symbols—track carefully.
  • Check direction in shifts: +2 shift (C→E) ≠ –2 shift (C→A).
  • In symbol coding: Always translate before applying logic.

Examples

Example 1 — Letter Shift

If CAT = DBU, then DOG = ?
Rule: +1 shift → D→E, O→P, G→H → Answer: EPH

Example 2 — Number Coding

If A = 1, B = 2, …, Z = 26, then code for “SUN” = 19 21 14.

Example 3 — Symbol Coding

If A # B means A is father of B, and A % B means A is sister of B, then:
P # Q % R → P is father of Q, and Q is sister of R → P is father of R.

Example 4 — Conditional Coding

If “+” means ×, “–” means ÷, “×” means –, and “÷” means +, then:
8 + 2 – 4 × 3 ÷ 5 = (8×2) ÷ 4 – 3 + 5 = 16 ÷ 4 – 3 + 5 = 4 – 3 + 5 = 6.

PRACTICE QUESTIONS
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