🧠 Coding and Decoding – Logical Reasoning

📌 What is Coding and Decoding?

Coding is a method of transmitting a message in such a way that only the intended person can understand it.
Decoding is the process of interpreting or converting the coded message back into its original form.

In reasoning questions, coding-decoding tests your ability to:

• Recognize letter/number patterns
• Understand symbol-language mapping
• Decode logic used in word or number transformations

🎯 Why It’s Important

• Appears frequently in logical reasoning sections of competitive exams
• Tests mental sharpness, logic, and observation skills
• Enhances analytical thinking and pattern recognition

📚 Types of Coding-Decoding Questions

1. Letter Coding

One word is coded as another using a pattern of letters.

Example: If TABLE is coded as UBCMF, how is CHAIR coded?

Solution: T→U (+1), A→B (+1), B→C (+1), L→M (+1), E→F (+1) → CHAIR → DIBJS ✅

2. Number Coding

Words are coded into numbers based on letter positions or patterns.

Example: If DOG is coded as 4157, how is CAT coded?

Solution: D=4, O=15, G=7 → C=3, A=1, T=20 → Answer: 31120

3. Substitution Coding

Words are replaced with other words or symbols, like a secret language.

Example: If 'blue' is called 'green', 'green' is called 'red', what is the color of grass?

Answer: Grass is normally green → 'green' is coded as 'red' → Answer = red

4. Letter Position Coding (Alphabetical Series Logic)

Each letter's position is used in logic (A = 1, B = 2, ..., Z = 26).

Example: If ACE = 135, what is BDF?

Solution: B=2, D=4, F=6 → Answer: 246

5. Mixed Coding (Coding by Sentences)

Full sentences are coded using random words or symbols.

Example:
"Ram eats mango" → "mi lo ta"
"mango is sweet" → "ta ki su"
What is the code for “mango”?
✅ Common word = “mango” → common code = ta

6. Matrix Coding

A matrix of letters/numbers is used for finding codes.

Example: Matrix with rows and columns, you are told to find the letter at Row 2, Column 3, etc.
(Used rarely, more common in advanced reasoning.)

✅ Common Tricks and Tips

Tip	Description
🔤 Learn A–Z letter positions	A=1, B=2 … Z=26
🔁 Watch for +1, -1 shifts	Many codes use shifting
🔁 Reverse letters	e.g., A ↔ Z, B ↔ Y
🔄 Pair words and codes carefully	Match positions accurately
📏 Break long words	Split word to find sub-patterns
🧪 Practice substitution puzzles	Build speed and accuracy

🧩 Sample Practice Questions

Q1:

If "GOLD" is written as "HPME", how is "SILVER" written?

Solution:
GOLD → G→H, O→P, L→M, D→E
SILVER → S→T, I→J, L→M, V→W, E→F, R→S
👉 Answer: TJMWFS

Q2:

If "DELHI" is coded as "73541" and "CALCUTTA" as "82589666", what is the code for "LITCHI"?

Solution:
From DELHI: D=7, E=3, L=5, H=4, I=1
From CALCUTTA: C=8, A=2, U=9, T=6
LITCHI → L=5, I=1, T=6, C=8, H=4, I=1 → Answer: 516841

💡 Advanced Coding Patterns

Pattern	Example
Mirror letters (A ↔ Z, B ↔ Y...)	HELLO → SVOOL
Skip coding (+2 or -2)	CAT → ECV
Reverse and code	CAT → TAC → UBS
Symbol mapping	CAT → #$@ (pre-defined mapping)

🏁 Conclusion

Coding and decoding improves:

• Vocabulary
• Logic building
• Observation skills
• Pattern recognition

✅ It’s all about logic + practice.