Coding-Decoding: CMAT Logical Reasoning Essentials

2026-06-14

Introduction

Coding-Decoding is a fundamental topic in the CMAT Logical Reasoning section that tests your ability to identify rules governing a transformation of information. These questions involve transforming words or numbers into a specific format using a hidden pattern. Success in this topic depends on your speed in recognizing these patterns and your familiarity with alphabet positions.

Core Concepts

To excel, you must memorize the positional values of the English alphabet (A=1, B=2, ..., Z=26). Having this data instantly available reduces the time spent on every problem. You should also be comfortable working with the reverse alphabet positions (A=26, Z=1) and knowing which letters are opposites (e.g., A and Z, B and Y).

Common Coding Patterns

Recognizing the logic used by the examiner is the most critical step in solving these problems.

• Forward Shifting: Each letter is replaced by a letter that appears a fixed number of positions after it in the alphabet (e.g., $+2$ shift, $A \rightarrow C$).
• Backward Shifting: Each letter is replaced by a letter that appears a fixed number of positions before it (e.g., $-1$ shift, $B \rightarrow A$).
• Reverse Coding: The letters are written in reverse order, or the entire string is reversed.
• Substitution Coding: A specific word is given a code, and you must apply that same logic to a target word.
• Positional/Number Coding: Letters are replaced by their corresponding numeric position in the alphabet.

Worked Example

Question: If CAT is coded as ECV, how is DOG coded?

1. Analyze the relationship between CAT and ECV.
2. C ($3$) becomes E ($5$), which is $+2$.
3. A ($1$) becomes C ($3$), which is $+2$.
4. T ($20$) becomes V ($22$), which is $+2$.
5. Apply the same $+2$ logic to DOG:
   • D ($4$) $+ 2 = 6$ (F)
   • O ($15$) $+ 2 = 17$ (Q)
   • G ($7$) $+ 2 = 9$ (I)

The answer is FQI.

Exam Strategy

When you encounter a coding-decoding question:

• Write down the position of each letter immediately.
• Calculate the difference between the letters of the given word and the code.
• Check for alternating patterns (e.g., $+1, -1, +2, -2$).
• If the letter count changes (e.g., 3 letters become 6), the code might be doubling the letters or adding a constant value.

Quick Revision

• Memorize the alphabet positions early.
• Look for the simplest pattern first (constant shift).
• Check for reverse or mixed patterns if a constant shift does not fit.
• Always verify your logic on the second half of the given word if possible.

Practise these as timed MCQs to lock the pattern in.