Study Material — 11 PYQs (2023–2023) · Concept Notes · Shortcuts
SSC CPO Coding Decoding is a frequently tested subtopic — 11 previous year questions from 2023–2023 papers are included below with concept notes, key rules and shortcut tricks.
11 questions from actual SSC CPO papers · all shown free · click option to reveal solution
Exam Q 12023Previous Year Pattern
In a certain coding system, each letter is replaced by the letter that comes 3 positions after it in the English alphabet. For example, A is coded as D, B is coded as E, and so on. If a letter reaches beyond Z, it wraps around to the beginning (so X→A, Y→B, Z→C). Using this rule, how would the word 'PLAY' be coded?
Exam Q 22023Previous Year Pattern
In a code language, consonants are replaced by the next consonant (B→C, C→D, D→F, F→G, etc., skipping vowels), and vowels remain unchanged. What is the code for 'FRIEND'?
Exam Q 32023Previous Year Pattern
In a code, each letter is replaced by the letter 2 positions before it in the alphabet (B→Z, C→A, D→B, and so on, wrapping around). What is the code for 'DOG'?
Exam Q 42023Previous Year Pattern
In a certain code, each letter is replaced by a number: A=1, B=2, C=3, ..., Z=26. What is the numeric code for the word 'CAT'?
Exam Q 52023Previous Year Pattern
In a certain code, each letter is replaced by the letter that comes 3 positions after it in the English alphabet. For example, A is coded as D, B is coded as E, and so on. What is the code for the word 'HELLO'?
Exam Q 62023Previous Year Pattern
In a certain coding system, each letter is replaced by the letter that comes 3 positions after it in the English alphabet, and the positions wrap around (Z wraps to C). Additionally, vowels are replaced by the number corresponding to their position in the vowel sequence (A=1, E=2, I=3, O=4, U=5). Using this rule, what is the code for the word 'PHONE'?
Exam Q 72023Previous Year Pattern
In a certain code, each letter is replaced by the letter that comes 3 positions after it in the English alphabet. For example, A→D, B→E, etc. If a letter goes beyond Z, it wraps around (X→A, Y→B, Z→C). What is the code for the word 'LOGIC'?
Exam Q 82023Previous Year Pattern
In a code, each letter is replaced by the letter that is 5 positions after it, except for vowels which are replaced by the vowel 2 positions after them in the vowel sequence (A→I, E→O, I→U, O→A, U→E). What is the code for 'BELIEVE'?
Exam Q 92023Previous Year Pattern
In a code language, the position of each letter in a word is reversed, and then each letter is replaced by the letter 2 positions before it in the alphabet (with wraparound: A→Y, B→Z). What is the code for 'SMART'?
Exam Q 102023Previous Year Pattern
In a certain code, consonants are assigned numbers based on their position in the alphabet (B=2, C=3, D=4, etc.), and vowels are assigned as A=1, E=5, I=9, O=15, U=21. What is the numerical code for 'TRAIN'?
Exam Q 112023Previous Year Pattern
In a code language, vowels are replaced by the next vowel in sequence (A→E, E→I, I→O, O→U, U→A), and consonants remain unchanged. What is the code for 'PROBLEM'?
Concept Notes
Coding Decoding— Rules & Concept
Core ConceptRead this first — the foundation of the topic
Core Concept
In coding, each letter or word is replaced by another letter, number, or symbol following a fixed rule. In decoding, you reverse this process to find the original word or its coded form
Letter Shift Coding
Each letter moves forward or backward by a fixed number in the alphabet.
2. Number/Position Coding: Letters are replaced by their position numbers in alphabet.
3
Substitution Coding
Specific letters are replaced by other specific letters.
4
Mixed Letter Coding
Combination of different coding methods
Formula for Letter Shift Coding
If A=1, B=2, C=3... Z=26
Forward Shift: New Position = (Original Position + Shift Value)
Backward Shift: New Position = (Original Position - Shift Value)
If result > 26, subtract 26. If result < 1, add 26.
Exam PatternsWhat examiners ask — read before attempting PYQs
Recognition
SSC CGL typically asks 1-2 questions on coding decoding
Common formats include
- If CAT = DOG, then BAT = ?
- In a code language, CHAIR is written as FKDLU. How is TABLE written?
- If MONDAY is coded as 123456, then SUNDAY is coded as?
ShortcutsUse these to save 30–60 seconds per question
#1 - Position Gap Method:
Find the gap between original and coded letters for first 2-3 letters. Apply same gap to remaining letters. This works for 80% of shift coding questions.
Worked ExampleSolve this step-by-step before moving on
1
Step 1
Find the pattern
H → K (H=8, K=11, difference = +3)
O → R (O=15, R=18, difference = +3)
R → U (R=18, U=21, difference = +3)
S → V (S=19, V=22, difference = +3)
E → H (E=5, H=8, difference = +3)
2
Step 2
Pattern identified = Each letter shifts +3 positions
3
Step 3
Apply to TIGER
T → W (T=20, +3=23=W)
I → L (I=9, +3=12=L)
G → J (G=7, +3=10=J)
E → H (E=5, +3=8=H)
R → U (R=18, +3=21=U)
Answer: TIGER = WLJHU
Worked Example 2:
Question: If in a certain code, BRAIN is written as CQBJO, how is SMILE written?
1
Step 1
Analyze each position
B → C (+1)
R → Q (-1)
A → B (+1)
I → J (+1)
N → O (+1)
Apply to SMILE
S → T (+1)
M → L (-1)
I → J (+1)
L → M (+1)
E → F (+1)
Answer: SMILE = TLJMF
Shortcut Trick #2 - Reverse Alphabet Method:
If A→Z, B→Y, C→X pattern appears, use formula: Coded Letter Position = 27 - Original Letter Position.
Shortcut Trick #3 - Number Coding Quick Check:
For number codes, first check if numbers represent alphabetical positions (A=1, B=2...). If not, look for arithmetic progression patterns.
#1 Most Common Trap/Mistake:
Students often assume the same shift applies to all letters without checking each position carefully. Many codes use different shifts for different positions (like Example 2 above). Always verify the pattern for at least 3 letters before applying to the answer.
Additional exam tip: If the pattern seems too complex, try working backwards from answer options - this often saves precious time in competitive exams.
Key Points to Remember
Coding Decoding involves finding patterns in letter/number substitutions
Most common pattern: Each letter shifts by same number of positions in alphabet
Formula: New Position = Original Position + Shift Value (adjust for alphabet limits)
Always check pattern in first 3 letters before applying to entire word
Reverse alphabet coding: A=Z, B=Y, use 27 minus original position
Number codes often represent alphabetical positions (A=1, B=2, C=3)
Mixed patterns have different shifts for different letter positions
Position Gap Method works for 80% of shift coding questions
If pattern is complex, work backwards from answer options to save time
SSC CGL typically includes 1-2 coding decoding questions per paper
Exam-Specific Tips
A=1, B=2, C=3... Z=26 is the standard alphabetical position formula
Forward shift formula: New Position = Original Position + Shift Value
Backward shift formula: New Position = Original Position - Shift Value
Reverse alphabet coding formula: Coded Position = 27 - Original Position
If coded position exceeds 26, subtract 26 to get correct alphabet position
If coded position is less than 1, add 26 to get correct alphabet position
Common shift values in SSC exams are +3, +2, +1, -1, -2, -3
Mixed position patterns typically alternate between +1 and -1 shifts
60-Second Revision — Coding Decoding
Remember: Check pattern in first 3 letters before solving completely
Formula: Shift coding = Original Position ± Shift Value
Trap: Don't assume same shift for all positions - verify each letter
Shortcut: Use Position Gap Method for quick pattern recognition
Technique: Work backwards from options if pattern seems complex
Quick check: A=1 to Z=26 for number-based coding questions
Time saver: Reverse alphabet uses 27 minus original position formula