🔐 Coding-Decoding - Complete Theory

Master code patterns - the fastest-scoring reasoning topic!

🎯 What is Coding-Decoding?

Coding-Decoding tests your ability to:

• Identify patterns in letter/number substitutions
• Decode hidden messages
• Apply consistent rules to encode/decode words

Example:

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

Pattern: Each letter shifted +1
C → D, A → B, T → U
Apply to DOG: D → E, O → P, G → H

Answer: EPH

📐 Types of Coding-Decoding

1. Letter Shift Coding

2. Letter Replacement

3. Number/Symbol Coding

4. Conditional Coding

5. Substitution Coding

6. Mixed Pattern Coding

🔤 Letter Shift Coding

Pattern 1: Fixed Forward Shift

Rule: Each letter shifted by same fixed number forward

Example:

If APPLE is coded as DSSOH

Find pattern:
A → D (+3)
P → S (+3)
P → S (+3)
L → O (+3)
E → H (+3)

Pattern: Each letter +3

Quick Method:

Write alphabet positions:
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

For +3 shift:
A(1) → D(4)
B(2) → E(5)
C(3) → F(6)

Pattern 2: Fixed Backward Shift

Rule: Each letter shifted by same fixed number backward

Example:

If MANGO is coded as JXKDL

Find pattern:
M → J (-3)
A → X (-3, wraps around: A → Z → Y → X)
N → K (-3)
G → D (-3)
O → L (-3)

Pattern: Each letter -3

Wrap-around Rule:

When going backward from A:
A → Z → Y → X (continues from end)

When going forward from Z:
Z → A → B → C (continues from start)

Pattern 3: Alternate Letter Shift

Rule: Alternate letters have different shifts

Example:

If CAT is coded as DBS

C → D (+1, odd position)
A → B (+1, even position)
T → S (-1, odd position)

Pattern:
Odd positions: +1
Even positions: -1

OR could be:
1st letter: +1
2nd letter: +1
3rd letter: -1

Pattern 4: Reverse Order

Rule: Word written in reverse

Example:

If BANK is coded as KNAB

B A N K → K N A B
Simply reversed!

Pattern 5: Reverse + Shift

Rule: First reverse, then apply shift

Example:

If CAT is coded as UBD

Step 1: Reverse CAT → TAC
Step 2: Apply shift +1 → UBD

T → U (+1)
A → B (+1)
C → D (+1)

🔢 Number/Symbol Coding

Pattern 1: Letter to Number

Rule: Each letter assigned a number

Example:

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

APPLE coded as:
A(1) P(16) P(16) L(12) E(5) = 1-16-16-12-5

Could be written as: 116161125

Pattern 2: Positional Value

Rule: Position value from start/end of alphabet

Example:

If 'A' has position 1, 'B' has 2... 'Z' has 26

CAT:
C = 3
A = 1
T = 20

Code: 3-1-20 or 31120

Reverse Position:

If 'Z' has position 1, 'Y' has 2... 'A' has 26

CAT:
C (from Z) = 24
A (from Z) = 26
T (from Z) = 7

Code: 24-26-7

Pattern 3: Symbol Substitution

Rule: Letters replaced by symbols

Example:

If A=@, E=#, I=%, O=&, U=$

AUDIO:
A U D I O → @ $ D % &

💡 Solved Examples

Example 1: Simple Forward Shift

Q: If WORD is coded as ZRUG, how is PAGE coded?

Solution:

Step 1: Find pattern

W → Z
O → R
R → U
D → G

Check shift:
W(23) → Z(26) = +3
O(15) → R(18) = +3
R(18) → U(21) = +3
D(4) → G(7) = +3

Pattern: Each letter +3

Step 2: Apply to PAGE

P(16) → S(19) (+3)
A(1) → D(4) (+3)
G(7) → J(10) (+3)
E(5) → H(8) (+3)

Answer: SDJH

Example 2: Opposite Letter

Q: If DELHI is coded as WVOSR, what is the pattern? Code MUMBAI.

Solution:

Step 1: Find pattern

D(4) → W(23)
E(5) → V(22)
L(12) → O(15)
H(8) → S(19)
I(9) → R(18)

Check relationship:
D(4) + W(23) = 27 (always)
E(5) + V(22) = 27
L(12) + O(15) = 27

Pattern: Opposite letters!

A(1) ↔ Z(26) [sum = 27]
B(2) ↔ Y(25) [sum = 27]
C(3) ↔ X(24) [sum = 27]

Formula: Position + Opposite Position = 27
Opposite = 27 - Position

Step 2: Apply to MUMBAI

M(13) → N(14) [27-13=14]
U(21) → F(6) [27-21=6]
M(13) → N(14)
B(2) → Y(25) [27-2=25]
A(1) → Z(26) [27-1=26]
I(9) → R(18) [27-9=18]

Answer: NFNYZR

Example 3: Conditional Pattern

Q: In a code, vowels are replaced by next letter, consonants by previous letter. How is BREAD coded?

Solution:

Step 1: Identify vowels and consonants

BREAD:
B - consonant
R - consonant
E - vowel
A - vowel
D - consonant

Step 2: Apply rules

B (consonant) → A (-1)
R (consonant) → Q (-1)
E (vowel) → F (+1)
A (vowel) → B (+1)
D (consonant) → C (-1)

Answer: AQFBC

Example 4: Word-to-Number Sum

Q: If CAT is coded as 24, DOG as 26, what is BIRD?

Solution:

Step 1: Find pattern

CAT:
C(3) + A(1) + T(20) = 24 ✓

DOG:
D(4) + O(15) + G(7) = 26 ✓

Pattern: Sum of letter positions

Step 2: Apply to BIRD

B(2) + I(9) + R(18) + D(4) = 33

Answer: 33

Example 5: Mixed Pattern

Q: If MANGO is coded as 53 and APPLE is coded as 50, how is ORANGE coded?

Solution:

Step 1: Analyze

MANGO: M(13) A(1) N(14) G(7) O(15) = 50, but answer is 53
APPLE: A(1) P(16) P(16) L(12) E(5) = 50, matches!

MANGO calculation wrong. Let's try reverse positions:

MANGO (reverse positions):
M(14) A(26) N(13) G(20) O(12) = 85 ✗

Try different approach:
Maybe it's (sum of positions) + (number of letters) - 2?

MANGO: 50 + 5 - 2 = 53 ✓
APPLE: 50 + 5 - 5 = 50 ✓ (hmm, pattern unclear)

Or simpler: Count of letters matters
MANGO (5 letters): Sum + 3 = 50 + 3 = 53 ✓
APPLE (5 letters): Sum + 0 = 50 ✓

Pattern isn't clear. In exam, we'd check options!

Step 2: Calculate for ORANGE

ORANGE:
O(15) R(18) A(1) N(14) G(7) E(5) = 60

If pattern is sum + specific value based on word:
Try: 60 (most likely answer)

Answer: 60 (most probable)

Example 6: Letter Rearrangement

Q: If BOARD is coded as YBBEO, what is CHAIR?

Solution:

Step 1: Find pattern

BOARD → YBBEO

Compare letter by letter:
Position 1: B → Y
Position 2: O → B
Position 3: A → B
Position 4: R → E
Position 5: D → O

Not a simple shift. Check rearrangement:
B O A R D
Y B B E O

Hmm, let's check if letters moved positions:
BOARD positions: 1 2 3 4 5
D moved to position 5? No, O is at 5

Try reverse + shift:
BOARD reversed = DRAOB
D R A O B
Apply -5 shift?
D(4) → Y(-1, wrap = 25) Nope

Let's check opposite + rearrange:
B(2) opposite = Y(25) ✓
O(15) opposite = L? No, code shows B

Pattern might be complex. Check first/last:
First letter B → opposite Y ✓
Second letter O → stays in code ✓

Without clear pattern, skip in exam or check answer options!

⚡ Quick Patterns to Recognize

Pattern 1: EJOTY Rule

Divide alphabet into 5 groups of 5 letters (plus Z):

E group: A B C D E (positions 1-5)
J group: F G H I J (positions 6-10)
O group: K L M N O (positions 11-15)
T group: P Q R S T (positions 16-20)
Y group: U V W X Y (positions 21-25)
Z: separate (position 26)

Example: Replace each letter with last of its group
A → E, B → E, C → E, D → E, E → E
F → J, G → J, etc.

Pattern 2: Alphabetical Position Formula

Forward Position:

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

Backward Position (from Z):

A=26, B=25, C=24... Z=1

Formula: Backward = 27 - Forward

Opposite Letter:

A ↔ Z, B ↔ Y, C ↔ X, D ↔ W...

Formula: Opposite letter position = 27 - Current position

⚠️ Common Mistakes

❌ Mistake 1: Not Checking Wrap-Around

Wrong: Z + 2 = error ✗
Right: Z + 2 = B (Z → A → B, wraps around) ✓

❌ Mistake 2: Mixing Forward/Backward

Wrong: Position of C from start = 24 ✗
Right: Position of C from start = 3 ✓
       Position of C from end = 24 ✓

❌ Mistake 3: Ignoring Pattern Type

Wrong: Assuming all questions use simple +n shift ✗
Right: Identify exact pattern first (could be reverse, opposite, conditional) ✓

❌ Mistake 4: Not Verifying with All Letters

Wrong: Find pattern with first 2 letters only ✗
Right: Verify pattern with ALL letters in the example ✓

📝 Practice Problems

Level 1: Basic Shift

1. If ROSE is coded as TQUG, how is LEAF coded?

2. If CAR is coded as 24, what is BUS?

3. If A=1, B=3, C=5 (odd positions), what is F?

Level 2: Medium

4. If TEACHER is coded as VGCEJGT, what is STUDENT?

5. If GRAPE is coded as 42, MANGO is 34, what is ORANGE?

6. In a code, first letter +2, second -1, third +2, fourth -1. Code EXAM.

Level 3: Hard

7. If in a language, vowels are coded as next vowel (A→E→I→O→U→A cycle), and consonants by opposite letter, code EDUCATION.

8. If BRILLIANT is coded as 1948938214, using A=1 to Z=26, what is LANGUAGE?

9. If MADRAS is coded as 112 and CALCUTTA is coded as 82, what is DELHI?

🎯 Exam Strategy

Time Management:

• Per question: 30-45 seconds
• For 5 coding questions: 2.5-3.5 minutes

Quick Approach:

1. Identify pattern (20 sec)
   • Check first 2-3 letters for shift/opposite/reverse
2. Verify pattern (10 sec)
   • Apply to remaining letters in example
3. Apply to target word (10 sec)
4. Match with options (5 sec)

Priority:

• ✅ Simple shift (±n) - 25 sec
• ✅ Opposite letters - 30 sec
• ✅ Reverse order - 20 sec
• ⏭️ Complex mixed patterns - 60+ sec (skip if unclear)

🔗 Related Topics

Uses Concepts From:

• Pattern recognition
• Basic arithmetic (for number codes)
• Alphabet positioning

Related Reasoning Topics:

• Alphanumeric Series - Pattern sequences
• Number Series - Number patterns

Practice:

• Coding-Decoding Questions

Master Coding-Decoding - Find the pattern, verify, apply! 🔐