Study Material — 1 PYQs (2024–2024) · Concept Notes · Shortcuts
RRB NTPC Coding Decoding is a frequently tested subtopic — 1 previous year questions from 2024–2024 papers are included below with concept notes, key rules and shortcut tricks.
1 questions from actual RRB NTPC papers · all shown free · click option to reveal solution
Exam Q 12024Previous 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 'HELP'?
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
Practice MCQs
Coding Decoding — Practice Questions
14graded MCQs · easy to hard · full solution & trap analysis
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 'BRAIN'?
Practice 2easy
In a code, each letter's position in the alphabet is replaced by a number (A=1, B=2, C=3, ..., Z=26). What is the numeric code for the word 'CAT'?
Practice 3easy
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?
Practice 4easy
In a code language, every alternate letter starting from the first letter is replaced by the letter that comes 1 position before it in the alphabet, while other letters remain unchanged. What is the code for 'GARDEN'?
Practice 5easy
In a certain code, consonants are shifted forward by 2 positions (B→D, C→E, etc.) and vowels are shifted backward by 1 position (A→Z, E→D, I→H, O→N, U→T). What is the code for 'SMILE'?
Practice 6medium
In a coding system, each letter is replaced by the letter that comes 3 positions after it in the alphabet (with wrapping: X→A, Y→B, Z→C). Using this rule, what is the code for the word 'LOGIC'?
Practice 7medium
In a certain code language, each letter is replaced by the letter that is 3 positions ahead in the alphabet (Z wraps to C, Y wraps to B, X wraps to A). Using this rule, what is the code for the word 'MASTER'?
Practice 8medium
In a certain coding system, each letter is replaced by the letter that comes 3 positions after it in the alphabet, and spaces are replaced by the symbol '@'. Using this rule, if HELLO WORLD is coded as KHOOR@ZRUOG, what will be the code for FRIEND?
Practice 9medium
A code uses the following pattern: for each letter, write its position in the alphabet. Then, if the position is odd, add 1; if the position is even, subtract 1. What is the code for 'MODERN'?
Practice 10medium
In a symbol-based code, each letter is assigned a symbol based on this rule: consonants are represented by their position number in the alphabet, and vowels are represented by the symbol of the consonant that comes immediately before them in the alphabet. For example, E comes after D, so E is coded as 4 (D's position). What is the code for 'SYSTEM'?
Practice 11medium
A word is coded using the following rule: reverse the word, then replace each letter with the letter 2 positions before it in the alphabet (A→Y, B→Z, C→A, D→B, etc.). What is the code for 'PRINT'?
Practice 12medium
In a number-substitution code, vowels are replaced as follows: A=1, E=5, I=9, O=6, U=3. Consonants are replaced by their position in the alphabet (B=2, C=3, etc.). What is the numeric code for 'BRAIN'?
Practice 13hard
In a coding system, each letter is replaced by the number representing its position in the alphabet, then each number is reversed (written backwards). Finally, all reversed numbers are added together. For example, if the word is 'CAB', then C=3, A=1, B=2. After reversal: 3→3, 1→1, 2→2. Sum = 3+1+2 = 6. Using this rule, what is the code for the word 'PRIZE'?
Practice 14hard
In a hybrid code, each letter is assigned a number (A=1, B=2, ..., Z=26). Then, the number is split into tens and units digits. The tens digit is replaced by a symbol (0→*, 1→@, 2→#), and the units digit is replaced by a letter (0→A, 1→B, 2→C, ..., 9→J). For example, M=13 splits to 1 and 3, giving @D (since 1→@ and 3→D). What is the hybrid code for 'QUIZ'?
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