Coding Decoding – General Aptitude for GATE, PSU, ESE, AE/JE | Priyanka Ma’am

Coding Decoding is an important topic in General Aptitude and is frequently asked in GATE, PSU, ESE, AE/JE exams. It tests your logical reasoning and pattern recognition ability.

Basic Concepts

Coding Decoding involves transforming words, letters, or numbers based on a specific pattern or rule.

• Coding: Converting original information into coded form
• Decoding: Finding the original meaning from coded form

Types of Coding Decoding

• Letter Coding
• Number Coding
• Substitution Coding
• Mixed Coding

Important Concepts

1. Alphabet Position

A = 1, B = 2, C = 3, ... Z = 26

2. Reverse Alphabet

A ↔ Z, B ↔ Y, C ↔ X

3. Letter Shifting

Letters may be shifted forward or backward by fixed positions.

4. Number Conversion

Words may be converted into numbers using alphabet positions.

Solved Examples

Example 1

If CAT is coded as DBU, how is DOG coded?

C→D (+1), A→B (+1), T→U (+1
D→E, O→P, G→H → EPH

Example 2

If BAT = 23, how is CAT coded?

B=2, A=1, T=20 → 2+1+20 = 23
C=3, A=1, T=20 → 3+1+20 = 24

Example 3

If ABC is coded as 123, DEF is coded as 456, then what is BAD?

B=2, A=1, D=4 → 214

Example 4

If FLOWER is coded as EKNVDQ, how is GARDEN coded?

Pattern: Each letter −1
G→F, A→Z, R→Q, D→C, E→D, N→M → FZQCDM

Shortcut Tricks

• Check letter positions first
• Look for shifting pattern (+/-)
• Try reverse alphabet logic
• Break word into individual letters

Questions

Q1. If PEN = 35, find BOOK.

P=16, E=5, N=14 → 35
B=2, O=15, O=15, K=11 → Total = 43

Q2. If ABC → DEF, then XYZ → ?

X→A, Y→B, Z→C → ABC

Exam Tips

• Memorize alphabet positions
• Practice different patterns regularly
• Check both forward and backward logic
• Avoid overthinking, keep it simple

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