SSC CGL Preparation – Day 17

Reasoning – Coding-Decoding (Repeated)

🔍 What is Coding-Decoding?

In this topic, a word, letter, or number is coded using a pattern or rule. Your job is to decode the pattern and answer questions based on it.

SSC CGL commonly asks both simple letter substitution and advanced logic-based patterns.

---

🧠 Types of Coding-Decoding

Type	Description
1. Letter Coding	Each letter in a word is replaced by another letter
2. Number Coding	Words are coded into numbers using positional or arithmetic logic
3. Substitution Coding	Words are replaced with completely new ones
4. Symbol/Pattern-Based Coding	Symbols or positions are involved
5. Matrix Coding (Box Coding)	Coding from a grid/matrix
6. Mixed Coding or Language Coding	Multiple statements coded using overlapping logic

---

📘 1. Letter Coding

➡️ Letters are coded based on alphabetical positions, either:

• Forward (A=1, B=2, …, Z=26)
• Reverse (Z=1, Y=2, …, A=26)

🧪 Example:

If BIG = DJI, then how is DOG coded?

Solution:
B → D (+2),
I → J (+1),
G → I (+2)
Pattern: +2, +1, +2
Apply to DOG:
D → F, O → P, G → I
✅ Answer: FPI

---

📘 2. Number Coding

➡️ A word is converted into a number using logic like:

• Positional value of letters
• Sum or difference of values
• Reverse letters

🧪 Example:

If CAR = 24, BUS = 42, find the logic.

C (3) + A (1) + R (18) = 22
B (2) + U (21) + S (19) = 42
Hence, sum of letter positions = number code

---

📘 3. Substitution Coding

➡️ In a sentence, words are replaced with other words.

🧪 Example:

“If ‘blue’ means ‘sky’, ‘green’ means ‘grass’, and ‘yellow’ means ‘sun’,” what does ‘blue and green’ mean?

✅ Answer: sky and grass

---

📘 4. Symbol/Pattern Coding

➡️ Symbols represent letters or combinations.

🧪 Example:

If
@ = A, $ = B, # = C
Then what does @$# mean?

✅ Answer: ABC

---

📘 5. Matrix Coding (Box Coding)

➡️ A table (matrix) contains letters, and a code is formed using row-column pairings.

🧪 Example:

	C1	C2	C3
R1	A	D	E
R2	B	C	F

Code for E? → R1C3 → 13

---

📘 6. Mixed Coding / Language Coding

➡️ Multiple statements coded using a shared logic.

🧪 Example:

Statements:

• “Apple is sweet” → ro pi ta
• “Banana is sweet” → so ro ta
  What is the code for “Apple”?

✅ Answer: Compare common codes → “is sweet” = ro, ta
→ “Apple” = pi

---

🔑 Tips to Crack Coding-Decoding in SSC CGL

Tip	Explanation
🔤 Learn A-Z positions	A=1, B=2, …, Z=26
🔁 Watch for patterns	Try +1, -1, reverse, alternate
➕ Try letter sum logic	Especially for number coding
👀 Eliminate wrong options	Often quicker than decoding fully
✍️ Practice mapping	Use rough space to list out positions

---

❗ Common Traps in SSC Exams

Trap	Strategy
Assumption-based answers	Stick to the exact pattern
Not checking reverse order	Test both forward/reverse logic
Ignoring letter position	Use positional values regularly
Missing hidden repetition	Look for symmetrical/alternate logic

---

🧠 Must-Practice Coding Logics

1. +2, -1, +3 patterns
2. Even-Odd swaps
3. Mirror Alphabet (A-Z, B-Y…)
4. Backward coding
5. Position-based sums or gaps