39  Coding and Decoding

39.1 Introduction

Coding and Decoding questions test your logical ability to interpret and transform information. A word, number, or symbol is coded based on a rule, and you are asked to decode it or apply the same rule elsewhere. These problems check reasoning, observation, and pattern recognition.

39.2 1) Types of Coding

39.2.1 1.1 Letter Coding

Words are coded by replacing letters with other letters, shifting alphabet positions, or reversing order.

Example:
WORD → XPSE (each letter +1 shift).
If CAT is coded as DBU, then DOG is coded as EPH.

39.2.2 1.2 Number Coding

Words, letters, or phrases are represented by numbers.
- Sometimes based on alphabet positions (A=1, B=2, … Z=26).
- Sometimes by arithmetic operations.

Example:
If CAT = 3+1+20 = 24, then DOG = 4+15+7 = 26.

39.2.3 1.3 Substitution Coding

Words are replaced with other words. You must decode the substitution.

Example:
“If ‘book’ is called ‘pen’, and ‘pen’ is called ‘pencil’…” then “What do you write with?” → Answer: pencil.

39.2.4 1.4 Mixed Coding

Different words are coded by symbols or random numbers, and you infer meaning by comparing statements.

Example:
1. “bo ra ka” means “good boy plays”.
2. “ra ta la” means “boy is smart”.
Common word “ra” → “boy”.

39.2.5 1.5 Symbol Coding

Symbols replace letters, words, or numbers.

Example:
If A = @, B = #, C = $, then CAB = $@#.

39.2.6 1.6 Mathematical Coding

Numbers or words are coded using arithmetic rules.

Example:
If 246 → 357 (each digit +1), then 135 → 246.

39.3 2) Common Coding Rules

  1. Alphabet shifting: forward (+n) or backward (−n).
  2. Reverse order: read backwards.
  3. Interchange: swap positions of letters.
  4. Positional value: use A=1, … Z=26.
  5. Word/letter substitution: one word stands for another.
  6. Mathematical operations: addition, multiplication, square, cube, etc.

39.4 3) Solved Examples

39.4.1 Example 1

If in a certain code, CAT = DBU, what is DOG?
- Rule: +1 shift in letters.
- DOG → EPH.

39.4.2 Example 2

In a code, A=1, B=2, … Z=26. If LION = 50, what is TIGER?
- LION = 12+9+15+14 = 50.
- TIGER = 20+9+7+5+18 = 59.

39.4.3 Example 3

If “bo ra ka” = “good boy plays” and “ra ta la” = “boy is smart”, what does “ra” mean?
- Common word = “boy”.

39.4.4 Example 4

If 321 is coded as 432, 654 is coded as 765, then 987 is coded as?
- Rule: add 1 to each digit.
- 987 → 1098.

39.5 4) Practice Questions

  1. If APPLE = BQQMF, then MANGO = ?
  2. In a code, ROAD = 43, then RAIL = ? (A=1, … Z=26, sum of letters).
  3. If “ti ra lo” = “sky is blue”, and “lo mi ta” = “sea is blue”, what does “lo” stand for?
  4. If 345 → 678, then 789 → ?
  5. If “star” = “moon”, “moon” = “sun”, then what shines at night?

39.6 5) Answer Key

  1. MANGO → NBOHP (each letter +1).
  2. ROAD = 18+15+1+4 = 38 (but given as 43, +5 adjustment). RAIL = 18+1+9+12 = 40+5 = 45.
  3. “lo” = “blue” (common).
  4. 789 → 101112 (each digit +3).
  5. Answer = “sun” (since “moon” is coded as “sun”).

39.7 Summary

  • Coding questions rely on shifts, substitutions, arithmetic, or symbols.
  • Always check for alphabet positions, addition/subtraction, or word substitutions.
  • Compare multiple statements to find common patterns.
  • Practice improves recognition speed and accuracy.