Coding-Decoding Guide & Practice

Foundation & Concepts

Coding is the process of encrypting a word, letter, or sentence based on a specific set of rules or patterns. Decoding is the reverse process of deciphering the code to find the original meaning.

1. Alphabetical Positioning

To solve coding-decoding questions, it is essential to remember the positions of letters in the English alphabet:

• Forward Order: A=1, B=2, ..., Z=26.
• Backward Order: Z=1, Y=2, ..., A=26.

Helpful Tools:

• EJOTY: (Forward: 5, 10, 15, 20, 25)
  • E=5, J=10, O=15, T=20, Y=25.
• CFILORUX: (Forward: 3, 6, 9, 12, 15, 18, 21, 24)
• Backward Order Calculation: Backward Position = 27 - Forward Position.

2. Circular Arrangement

Think of the alphabet as a circle. One step forward from Z is A; one step backward from A is Z. This is crucial for shift-based coding.

Patterns/Rules

1. Letter-to-Letter Coding: Letters are shifted (e.g., +2, -3) or interchanged based on position.
2. Letter-to-Number Coding: Numerical values are assigned based on positional value, sum of values, or arbitrary mapping.
3. Substitutional Coding: Words are replaced by other words (e.g., "Blue is called Red").
4. Chinese/Sentence Coding: Deciphering common words across multiple coded sentences to find individual codes.
5. Conditional Coding: Codes are assigned based on specific conditions (e.g., "If first letter is a vowel and last is a consonant...").
6. Binary/Clock Coding: Numbers or time units are converted into symbols or binary digits (0 and 1).