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 Pattern 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?
Shortcut Trick #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 Example 1
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
Pattern identified = Each letter shifts +3 positions
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
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.
In a certain code, every alternate letter (starting from the 1st letter) is shifted forward by 1 position in the alphabet, while the remaining letters stay unchanged. For example, 'ABCD' is coded as 'BBCD' (A→B at position 1, B stays at position 2, C→D at position 3, D stays at position 4). What is the code for 'PENCIL'?
Practice 2easy
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 (e.g., Y becomes B, Z becomes C). Using this rule, how will the word 'PRINT' be coded?
Practice 3easy
In a code language, consonants are replaced by the consonant that comes 2 positions after them (B→D, C→F, D→F, etc.), and vowels are replaced by the symbol '*'. Using this rule, what is the code for 'SMILE'?
Practice 4easy
In a certain code, each letter is assigned a number based on its position in the alphabet (A=1, B=2, C=3, ..., Z=26). A word is encoded by writing the numbers of its letters in reverse order. For example, 'CAT' is encoded as 20-1-3 (because T=20, A=1, C=3). What is the code for 'DOG'?
Practice 5easy
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. Using this rule, what is the code for the word 'BRAIN'?
Practice 6easy
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. If the word 'HELLO' is coded using this rule, what will be the code?
Practice 7medium
In a certain code, each letter is assigned a number: A=1, B=2, C=3, ..., Z=26. A word is encoded by writing the numbers of its letters in reverse order. For example, 'CAT' is encoded as 20-1-3 (because T=20, A=1, C=3). What is the code for 'BRAIN'?
Practice 8medium
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 'FRIEND'?
Practice 9medium
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 code, what is the encoding of the word 'PHONE'?
Practice 10medium
In a code language, each letter is replaced by a symbol based on this rule: vowels (A, E, I, O, U) become *, and consonants become the number representing their position in the consonant sequence (B=1, C=2, D=3, F=4, G=5, H=6, J=7, K=8, L=9, M=10, N=11, P=12, Q=13, R=14, S=15, T=16, V=17, W=18, X=19, Y=20, Z=21). What is the code for 'MARKET'?
Practice 11medium
In a certain code, each letter is replaced by the letter that comes 3 positions ahead in the English alphabet. For example, A→D, B→E, C→F, and so on. Z wraps around to C. Using this rule, what is the code for the word 'LOGIC'?
Practice 12hard
In a coding system, each letter is replaced by the number representing its position in the alphabet, then each number is multiplied by 2 and decreased by 1. For example, A (position 1) becomes 1×2−1=1, B (position 2) becomes 2×2−1=3. If the word 'LOGIC' is encoded using this rule, what is the sum of all encoded values?
Practice 13hard
A reverse-substitution code works as follows: first, replace each letter with its reverse position in the alphabet (A↔Z, B↔Y, C↔X, etc.), then reverse the entire word. For example, 'BAD' becomes 'YZW' (B→Y, A→Z, D→W), then reversed to 'WZY'. Using this rule, if the code for a word is 'ZYXWVU', what is the original word?
Practice 14hard
In a positional-shift code, each letter in a word is replaced by the letter that is (position of letter in word) places ahead in the alphabet. For example, in 'CAT', C is at position 1, so C→D (1 place ahead); A is at position 2, so A→C (2 places ahead); T is at position 3, so T→W (3 places ahead), giving 'DCW'. Using this rule, what is the code for 'SYMBOL'?
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