Coding - Decoding
🔒 Log in to trackCoding questions reveal how a word (or sentence) is transformed into a code and ask you to apply the same transformation to a new word. CGL asks 3-5 per shift. Rules are mechanical: letter shifts, opposites, reversal, position sums, renames. Compute the rule from the sample pair, then apply it without creativity.
One page per subtopic: detailed notes, every question type, formulas, tricks and practice sets.
Every formula on one printable page, grouped by subtopic.
4 exam-level questions worked step by step.
93 questions — untimed practice or a timed test with analysis.
Track record in the exam
Questions per shift in recent SSC CGL papers.
Test difficulty mix (93 questions)
Question patterns exams keep repeating
Taken from previous-year papers. If a pattern is marked "very common", expect to see it in your exam.
Letter-shift coding of a new word
very commonA sample word and its code are given ('If PEN is written as RGP...'). Every letter of the code is a fixed number of places ahead of or behind the original letter, or the shift changes slot by slot.
How to solve: Write the shift under each letter of the sample (e.g. +2, +2, +2). Apply exactly the same shifts to the new word. Remember that after Z you come back to A.
Example: If PEN is written as RGP, how is RING written?
P→R, E→G, N→P: +2 each. R+2 = T, I+2 = K, N+2 = P, G+2 = I → TKPI.
Decoding: find the original word
commonThe code of the new word is given and the real word is asked ('Which word is written as TKPI?').
How to solve: Find the rule from the sample, then run it backwards: subtract where the rule adds, un-reverse where it reverses. Check the answer by coding it forward once.
Example: If PEN is written as RGP, which word is written as TKPI?
The rule is +2, so decode with −2: T→R, K→I, P→N, I→G → RING.
Reversal and reverse-plus-shift coding
commonRead the code from right to left. If you see the original word, or the original word with every letter moved by the same amount, the rule contains a reversal.
How to solve: Reverse the new word, then apply the same shift as the sample. Keep the same order of steps (reverse then shift, or shift then reverse) that the sample used.
Example: If GOLD is written as EMPH, how is SILK written?
GOLD +1 = HPME; reversed = EMPH ✓. SILK +1 = TJML; reversed = LMJT.
Opposite-letter coding
commonEach code letter and its original letter add up to 27 in position (A↔Z, M↔N). Codes look 'far away' from the word, e.g. MILK → NROP.
How to solve: Confirm the 27 total on two letters, then write the opposite of each letter of the new word. If the code is also reversed, reverse at the end.
Example: If MILK is written as NROP, how is CAKE written?
M(13)+N(14) = 27, so opposite letters. C↔X, A↔Z, K↔P, E↔V → XZPV.
Word to number coding
very commonA word is given a number ('BAT = 23'). The number is built from alphabet positions: plain sum, sum plus/minus or times a constant, weighted sum, reverse positions, or the letter positions written side by side.
How to solve: Find the plain position sum of the sample first and compare it with the code. The gap (+k, ×k, or a letter-count link) is the rule. Apply the same rule to the new word.
Example: If BAT = 23, what is CAR?
B+A+T = 2+1+20 = 23, a plain sum. C+A+R = 3+1+18 = 22.
Substitution (renaming) chains
common'Sky is called sea, sea is called water...' followed by a real-life question such as 'where do fish live?'
How to solve: First answer the real-life question in your head (fish live in the sea). Then give the code name of that answer (sea is called water) — rename exactly once.
Example: If milk is called water, water is called juice and juice is called tea, what do we drink when thirsty?
Real answer: water. 'Water' is called juice in this code.
Language coding with common words
very commonTwo to four sentences with jumbled code words ('good morning sir' = 'pa ka ni'); code of one word asked, or 'which could be the code', or 'cannot be determined'.
How to solve: Take the sentences that contain the word, keep the code words common to all of them, remove codes already fixed for other words. One code left = answer; two left = cannot be determined.
Example: 'sun is hot' = 'ta mo ri' and 'sun is bright' = 'ri ze mo'. What is the code for 'bright'?
'sun is' ↔ 'ri mo' (common). Sentence 2 left over: bright ↔ ze.
Letter-to-symbol / digit coding
commonLetters or digits are replaced by symbols, either from a given table (sometimes with conditions) or from a few coded words that share letters.
How to solve: Match shared letters with shared symbols across the given words. For tables, check the conditions first, then code letter by letter.
Example: If ROSE = 6821 and SORE = 2861, what is the code for O?
The digits follow the letter order: R = 6, O = 8, S = 2, E = 1. Check: SORE = 2 8 6 1 ✓. So O = 8.
Rearrangement and mixed-rule coding
occasionalThe code uses the same letters as the word but in a new order (pairs swapped, halves reversed, first and last interchanged), or two rules act together (vowels +1 and consonants −1).
How to solve: Compare letter by letter: are the letters the same (rearrangement) or changed (shift)? For rearrangement, note which slot went where; for mixed rules, note which group of letters got which change.
Example: If PLANET is written as LPNATE, how is FOREST written?
Letters are swapped in pairs: PL→LP, AN→NA, ET→TE. FO→OF, RE→ER, ST→TS → OFERTS.