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
45graded MCQs · easy to hard · full solution & trap analysis · showing 20 of 45
In a code language, the position of letters in a word is reversed, and then each letter is replaced by the letter 2 positions before it in the alphabet (B→Z, C→A, D→B, etc., wrapping around). What is the code for 'PLAY'?
Practice 2easy
In a certain code language, each letter is replaced by the letter that comes 3 places after it in the English alphabet (A=D, B=E, C=F, ...). Using this rule, what is the code for the word 'COLD'?
Practice 3easy
In a certain code, each letter is replaced by a number: A=1, B=2, C=3, ..., Z=26. If 'CAT' is coded as 3-1-20, what is the code for 'DOG'?
Practice 4easy
In a code language, vowels (A, E, I, O, U) 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 'BRAIN'?
Practice 5easy
In a certain code, the first and last letters of a word are swapped, and all other letters remain in their original positions. For example, 'BOOK' becomes 'KBOO'. What is the code for 'PENCIL'?
Practice 6easy
In a code, each letter is replaced by a number: A=1, B=2, C=3, ..., Z=26. If 'CAT' is coded as 3-1-20, what is the code for 'DOG'?
Practice 7easy
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 the word 'BRAIN'?
Practice 8easy
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 is the coded word?
Practice 9easy
In a certain coding system, each letter is replaced by the letter that comes 3 positions ahead of 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 10easy
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 is the code?
Practice 11easy
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 the word HELLO is coded using this system, what will be the code?
Note: After Z, the sequence wraps around to A (i.e., X→A, Y→B, Z→C).
Practice 12easy
In a code, each letter is replaced by the letter that comes 2 positions before it in the English alphabet (B→Z wraps around). For example, C is coded as A. What is the code for 'FRIEND'?
Practice 13easy
In a certain code, 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 'MAKE'?
Practice 14easy
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 is the code?
Practice 15easy
In a code, each letter is replaced by the letter that comes 2 positions before it in the English alphabet. For example, C → A, D → B, and so on. Letters A and B wrap around to Y and Z respectively. Using this rule, what is the code for the word 'FRIEND'?
Practice 16easy
In a code, consonants are coded as the next consonant (B→C, C→D, D→F, F→G, etc., skipping vowels), and vowels are coded as the previous vowel (E→A, I→E, O→I, U→O, A→U). What is the code for 'FRIEND'?
Practice 17easy
In a code language, consonants are replaced by the next consonant (B→C, C→D, D→F, F→G, G→H, H→J, J→K, K→L, L→M, M→N, N→P, P→Q, Q→R, R→S, S→T, T→V, V→W, W→X, X→Y, Y→Z, Z→B), and vowels remain unchanged. What is the code for 'SMILE'?
Practice 18easy
In a code, consonants are numbered by their position in the English alphabet, and vowels are represented by symbols: A=@, E=#, I=$, O=%, U=&. What is the code for 'SYSTEM'?
Practice 19easy
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, and so on. Z wraps around to C. Using this rule, what is the code for the word 'HELLO'?
Practice 20easy
In a code, the word 'BOOK' is written as '2-15-15-11'. Each letter is replaced by its position number in the English alphabet (A=1, B=2, C=3, ... Z=26). Using this rule, how is the word 'CARE' coded?
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