Mental Reasoning 6- Coding and Decoding: Questions and Step-by-Step Solutions for Competitive Exams SSC, BSSC, Bank, Railways

Mental Reasoning 6- Coding and Decoding: Questions and Step-by-Step Solutions for Competitive Exams SSC, BSSC, Bank, Railways

Coding and Decoding — one of the most scoring topics in Mental Reasoning for exams like SSC, Banking, Railways, BPSC, NDA, CDS, etc.
I’ll explain:
1. Concept & approach
2. All probable types (covering maximum variations)
3. Tricks & step-by-step examples in Bilingual format (English + Hindi)
 
Mental Reasoning ( Non-Verbal Series)– Coding and Decoding

1. Concept (Basic Idea)
Coding and Decoding is a topic where words, numbers, or letters are converted into a code using a specific rule. You are required to decode, encode, or find relationships.
Exam Types:
Word-based
Number-based
Mixed (letters + numbers)
Example:
If CAT → DBU, then C→D, A→B, T→U → Each letter +1 → DOG → ? → EPH
Hindi:
Coding and decoding में शब्द या संख्या को एक नियम के अनुसार बदल दिया जाता है।
आपको इसका पैटर्न पहचानकर अगला कोड या वास्तविक शब्द/संख्या निकालना होता है।

2. How to Approach Coding/Decoding
Observe the given codes for letters/numbers.
Check letter positions in alphabet (A=1, B=2, … Z=26).
Look for patterns:
 
/ – shifts
Reverse order
Skip letters
Symbol substitution
Apply the same pattern to the new word/number.

3. Common & Probable Types
Here’s a complete list of likely patterns seen in competitive exams.

Type 1 – Letter Shifting / Substitution
Rule: Shift letters forward/backward by a fixed number.
Example:
WORD → XPSE (+1)
HELLO → ? (+1) → IFMMP
Hindi: अक्षरों को एक निश्चित संख्या आगे/पीछे बढ़ाया जाता है।

Type 2 – Reverse Coding
Rule: Word is written backward.
Example:
TABLE → ELBAT
DOG → GOD
Hindi: शब्द उल्टा लिखा जाता है।

Type 3 – Skip Letter / Alternate Letter Coding
Rule: Only alternate letters are coded or skipped.
Example:
MOTHER → NPUIFS (+1 for each letter)
LETTER → ? → MFUUFS

Type 4 – Number Substitution
Rule: Letters replaced by their position in the alphabet (A=1, B=2 … Z=26)
Example:
CAB → 3 1 2
DOG → 4 15 7
Hindi: अक्षर को उसके क्रमांक से बदलना।

Type 5 – Symbol Coding
Rule: Letters replaced with symbols, shapes, or numbers according to a key
Example:
A → #, B → @, C → & → ABC → #@&

Type 6 – Mixed Letter Coding
Rule: First letter +1, second –1, third +2 etc.
Example:
CAT → DBV (+1, +1, +2) → DOG → ? → EPH

Type 7 – Reverse + Shift
Rule: Reverse word and then shift letters.
Example:
TABLE → ELBAT → +1 → FMCBU

Type 8 – Substitution by Position in Word
Rule: 1st letter → 2nd position letter of alphabet, 2nd → 3rd, etc.
Example:
ABCD → B C D E

Type 9 – Coding by Grouping
Rule: Letters are grouped or paired, then coded.
Example:
COMPUTER → CO MP UT ER → Replace each pair with +1 → DP NQ VU FS

Type 10 – Coding by Counting / Mathematical Logic
Rule: Each letter = number of strokes or lines, then coded.
Example:
A(1) → B(2) → C(3) → Etc.

Type 11 – Symbolic Coding for Numbers
Rule: Numbers are coded using symbols or words.
Example:
1 → @, 2 → #, 3 → & → 123 → @#&

Type 12 – Opposite / Alphabetical Reverse
Rule: A → Z, B → Y, C → X …
Example:
CAT → XZG

Type 13 – Coding by Rearrangement (Jumbling)
Rule: Letters of word rearranged in a particular sequence
Example:
TABLE → BATE L → New code

Type 14 – Mixed Coding & Decoding
Combination of above rules in single question.
4. Tricks for Quick Solving
Check forward/backward shifts first.
Look for reversal.
Count letter positions in alphabet.
Observe alternating patterns (odd/even letters).
Check for numbers in code → likely numeric coding.
Practice with frequently recurring patterns.

5. Sample Questions -Non-verbal Series
Q1: If CAT → DBU, then DOG → ?
Step: Each letter +1
C→D, A→B, T→U
D→E, O→P, G→H → Answer: EPH
Hindi: प्रत्येक अक्षर +1 → उत्तर = EPH

Q2: If TABLE → ELBAT, then CHAIR → ?
Step: Reverse
C H A I R → R I A H C → Answer: RIAHC
Hindi: शब्द उल्टा → RIAHC

Q3: If A=1, B=2, … Z=26, then CAT → ?
C=3, A=1, T=20 → Answer: 3 1 20
Hindi: अक्षरों को क्रमांक से बदलें → 3 1 20

Q4: If HELLO → IFMMP, then WORLD → ?
+1 shift each letter
W→X, O→P, R→S, L→M, D→E → Answer: XPSME
Hindi: प्रत्येक अक्षर +1 → उत्तर XPSME

Q5: If CAT → XZG (A→Z, B→Y, …), then DOG → ?
D→W, O→L, G→T → Answer: WLT
Hindi: अक्षरों का उल्टा क्रम → WLT