Coding-Decoding is a reasoning technique in which a word or message is encrypted or transformed into a particular pattern or code and you are required to decipher the rule or decode the original message.
It's used to test:
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Logical thinking
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Pattern recognition
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Understanding of letter/number sequences
🧠 Types of Coding-Decoding Questions
1️⃣ Letter Coding
A word is coded by replacing each letter with another letter based on a rule (e.g., shifting forward or backward in the alphabet).
Example:
BOY → DQA
Rule: +2 shift for each letter: B→D, O→Q, Y→A
2️⃣ Number Coding
Words are represented in numeric form using alphabet positions or arithmetic logic.
Example:
CAT → 3 1 20
Rule: Use positions in the alphabet (C=3, A=1, T=20)
3️⃣ Substitution Coding
Words are replaced with other words arbitrarily. Based on a sentence or group of sentences, you must decode the meaning.
Example:
In a code language, "Sky is Blue" is written as "Mi Ki Ti".
Another: "Sea is Deep" is "Ki Zi Ni".
Find code for "is" → Ki
4️⃣ Mixed/Conditional Coding
Complex codes combining letters and numbers or patterns from multiple rules.
Example:
If:
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Pen is coded as QFO
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Book is coded as CPLL
Then what is code for Note?
5️⃣ Decoding (Reverse Coding)
You’re given the code and have to work backwards to find the original word.
🔤 Alphabet Positions Chart
| A | B | C | D | E | F | G | H | I | J | K | L | M |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 |
| N | O | P | Q | R | S | T | U | V | W | X | Y | Z |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 |
📘 Examples with Explanation
🟢 Example 1: Letter Coding
Q: If DOG is coded as FQI, what is the code for CAT?
→ D→F (+2), O→Q (+2), G→I (+2)
So, C→E, A→C, T→V
✅ Answer: ECV
🟢 Example 2: Number Coding
Q: If A=1, B=2, ..., Z=26, what is the sum of letters in the word SUN?
S=19, U=21, N=14
19 + 21 + 14 = ✅ 54
🟢 Example 3: Substitution Coding
Q:
“Roses are Red” → “Ti Ki Mi”
“Apples are Sweet” → “Ki Pi Zi”
What is the code for ‘are’?
Look for common word: “are” appears in both → code Ki
✅ Answer: Ki
🟢 Example 4: Decoding
Q: If FLOWER is written as GMPXFS, what is the original word?
G→F (–1), M→L (–1), P→O (–1), X→W, F→E, S→R
✅ Answer: FLOWER
📝 Tips and Tricks
🔹 Know alphabet positions (quick recall saves time)
🔹 Check for +1, +2 shifts or reverse coding
🔹 Compare positions of letters
🔹 Use options to verify answers when unsure
🔹 Watch for patterns in examples
❓ Practice MCQs
🔸 Q1:
If RAJ is coded as TCL, then what is the code for FUN?
a) HWP
b) HVO
c) EVM
d) GWQ
→ Answer: a) HWP
Explanation: +2 shift: F→H, U→W, N→P
🔸 Q2:
If LION = 12 9 15 14, then what is TIGER?
a) 20 9 7 5 18
b) 20 8 7 4 17
c) 19 8 6 5 18
d) 21 10 8 6 19
→ Answer: a) 20 9 7 5 18
Explanation: Alphabet positions
🔸 Q3:
If COLD is coded as DPME, what is the code for HEAT?
a) IFBU
b) IDBU
c) GBZU
d) GDAU
→ Answer: a) IFBU
Explanation: +1 shift for each letter
📚 Common Coding Patterns to Remember
| Pattern | Rule Example | Meaning |
|---|---|---|
| +1 | CAT → DBU | Add 1 to each letter |
| –1 | DOG → CNF | Subtract 1 from each |
| Reverse | ABC → CBA | Reverse the word |
| Mirror | A=Z, B=Y, ... | Mirror image letters |
| Position | A=1, Z=26 | Alphabet position |
🧾 Summary
✅ Coding-Decoding tests your:
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Logical pattern recognition
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Letter/number manipulation
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Vocabulary-based reasoning
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Speed and accuracy
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