Coding - Decoding
🔒 Log in to trackSymbol and digit coding
🔒 Log in to trackLetters (or digits) are replaced by symbols or digits, one fixed code per letter. Either a code table is given (sometimes with extra conditions), or you get a few words with their codes and must work out which symbol stands for which letter by matching common letters. Once a letter's code is known it never changes inside the question.
Detailed notes
What is symbol and digit coding?
Letters (or digits) are replaced by symbols (@ # % * ...) or digits, one fixed code per letter. Two exam looks:
- A table is given: M = #, A = @, T = %. Code the word letter by letter.
- No table: two or three words come with their codes, and you discover which symbol stands for which letter by matching.
Once a letter's code is known, it never changes inside the question.
Type 1: code straight from the table
Write the table's letter under each letter of the word, in order. If MAT has M = #, A = @, T = %, then MAT = #@%. Watch for extra conditions:
- "If the word begins with a vowel, write the codes in reverse order."
- "If the digit sum is even, reverse the digits first."
Check the condition before touching the table — the setter counts on you forgetting it.
Type 2: match common letters with common symbols
When two coded words share letters, their codes share exactly those symbols:
- PEN = @ # % and NET = % # &
- Common letters E, N sit at the same places as common symbols #, % → E = #, N = %.
- The leftover letter of PEN (P) takes the leftover symbol @.
This works when the symbols keep their positions. If the question says the symbol order may differ, match by count: two common letters must appear as two common symbols; the leftover pairs up one-to-one.
Digit tables
Digits may stand for letters with a simple build: A = 2, B = 4, C = 6 (double the position). Code letter by digit, keeping one digit per letter. 4 can be one letter (D) or part of 10 (J) — count letters, not digits.
Matrix coding (SSC favourite)
Letters sit in a 5 × 5 grid; rows and columns are numbered 1-5. Each letter's code is its (row, column) pair. Read the word letter by letter and write the pairs: H is in row 2, column 3 → 23. The code of a 4-letter word is four two-digit numbers.
Speed tip: the same letter may appear more than once in the grid in some papers — any valid position pair is accepted; pick the one that matches an option.
Conditions with numbers
Number codes come with a test: "if the sum of the digits is even, reverse the digits before coding." Sum first, then decide the order, then map digit → symbol.
Quick revision
- Table given: map letter by letter; check conditions first.
- No table: common letters ↔ common symbols; leftovers pair up.
- Symbols may not keep order — then only counts are safe, and two possible codes mean 'cannot be determined'.
- Matrix: code = (row, column) per letter; the grid has no J in the classic version.
- Mixed conditions: decide the order rule before coding anything.
Types of questions asked
Every way this subtopic shows up in exams — how to recognise it, the formula or logic to use, and a solved example.
Type 1: Direct table look-upvery common3 practice Q
A letter → symbol/digit table is printed with the question.
- Write the code symbol under each letter of the word, in order.
- Join the symbols without spaces (or as the options show).
- Double-check the table row you used.
Why it works: the table fixes every letter; nothing needs discovering.
Example: M = #, A = @, T = %. What is the code of MAT?
M → #, A → @, T → %. MAT = #@%.
Type 2: Condition before the tablecommon2 practice Q
The question lists conditions ('if the word begins with a vowel, reverse the codes') above the table.
- Test the conditions on the word in order.
- Apply the first matching condition (reverse order, swap rows ...).
- Only then code from the table.
Why it works: the condition changes the ORDER of symbols, not their letter values.
Example: Table: E = &, C = $, H = %, O = *. Condition: if the word begins with a vowel, write the codes in reverse order. Code of ECHO?
ECHO begins with the vowel E → reverse. Direct codes are & $ % *; reversed → *%$&.
Type 3: Match common letters ↔ common symbols (no table)common2 practice Q
Words like 'PEN = @ # %' and 'NET = % # &' come with no table; you must infer codes.
- Circle letters shared by two words and symbols shared by their codes.
- Pair them (position-wise when order is fixed).
- Left-over letter takes the left-over symbol.
Why it works: codes are letter-for-symbol, so shared letters force shared symbols.
Example: PEN = @ # %, NET = % # &. What is the code for P?
E and N are common; # and % are the common symbols → E = #, N = %. PEN's leftover P takes PEN's leftover @.
Type 4: Digit substitution for letterscommon3 practice Q
Letters map to digits by a rule (A = 2, B = 4, C = 6 ... or vowels to their positions).
- Find the build rule from the given examples (double the position, position itself ...).
- Convert the word letter by letter.
- Keep one number per letter — 10 takes two digit places.
Why it works: the build rule is a small arithmetic step on positions.
Example: A = 2, B = 4, C = 6 ... (double the position). What is the code of CAB?
C = 6, A = 2, B = 4 → 624.
Type 5: Matrix coding (row, column)very common2 practice Q
A 5 × 5 grid of letters with numbered rows and columns; the code of each letter is a two-digit (row, column) pair.
- Find each letter's row and column in the grid.
- Write the pair as two digits (row first, then column).
- Join the pairs for the whole word.
Why it works: the grid is just a table; the pair is an address.
Example: In the following 5 × 5 matrix, columns are numbered 1-5 from left to right and rows 1-5 from top to bottom: Row 1: A B C D E Row 2: F G H I K Row 3: L M N O P Row 4: Q R S T U Row 5: V W X Y Z What is the code for HIDE?
H = (2, 3), I = (2, 4), D = (1, 4), E = (1, 5) → 23, 24, 14, 15.
Shortcut tricks
⚡ Common letters ↔ common symbols
When two coded words share letters, their codes share exactly the same number of symbols. Circle the shared letters and the shared symbols — they belong to each other. What is left over in each word belongs to the left-over letters.
Example: Q. 'PEN' is coded '@ # %' and 'NET' is coded '% & #' (order of symbols may differ). What is the code for P?
Common letters E, N ↔ common symbols #, %. So P takes the remaining symbol of PEN → @ (and T = &).
⚡ Conditions before the table
In condition-type questions, first check the conditions on the letter group (first letter vowel? last letter consonant?). Only if no condition applies do you code straight from the table.
Where students lose marks
Assuming symbols appear in the same order as the letters when the question says the order may differ.
Coding straight from the table without first checking whether a condition applies.
Applying two conditions at once when the question says only the first matching condition applies.
Practice sets — 12 questions
Sets of 10, mixed across the question types above. Each answer comes with a step-by-step explanation.
Topic test · 12 questions
Suggested time 8 min · wrong answers go to your mistake notebook automatically.