Coding-Decoding
Coding-Decoding is a frequently tested area in CUET General Test. Work through these free NTA-style sample questions with full answers and explanations, then attempt all 40 in a timed practice test to build exam-day speed.
Snapshot
- Coding-Decoding disguises a word, number or message with a hidden rule and asks you to encode or decode something new. Crack the rule on the example you are given, then apply it mechanically.
- Almost everything rests on alphabet positions (A = 1 ... Z = 26) and the mirror rule (a letter and its opposite add to 27). Know both cold.
- CUET asks letter-shift codes, number codes, message (sentence) codes, substitution codes, symbol codes, conditional codes and operation-substitution questions.
- The safest habit: write the positions under every letter before you do anything else. Exam reality: +5 for a correct answer and −1 for a wrong one.
Part 1 — The alphabet toolkit and the method
Written and reviewed by Devendra Dubey, Mathematics & Commerce faculty at UniDrill (M.Sc. Mathematics, Osmania University · 10 years teaching). Prepared for the CUET UG General Test.
Letter codes are arithmetic on positions. Once every letter is a number from 1 to 26, the rule usually reveals itself within seconds.
| Fact | Detail |
|---|---|
| Anchor letters | A = 1, E = 5, J = 10, O = 15, T = 20, Y = 25 (EJOTY) |
| Mirror rule | A letter at position p has the opposite letter at 27 − p. A↔Z, B↔Y, C↔X, M↔N |
| Wrap-around | After Z (26) counting returns to A, so Y + 3 = B and B − 3 = Y |
| Vowels | A, E, I, O, U |
| Alphabet halves | A to M are positions 1 to 13; N to Z are 14 to 26 |
The five-step routine.
| Step | Action | Why |
|---|---|---|
| 1. Write positions | Put the position of each letter under it, both for the word and the code | The rule is visible in the numbers |
| 2. Compare letter by letter | Subtract word position from code position for each letter | A constant difference means a fixed shift |
| 3. Test the simple rules first | Fixed shift, mirror, reverse order, alternating shift | They cover most questions |
| 4. Confirm on the whole word | A rule that fits only three of five letters is wrong | Complete verification |
| 5. Apply to the new word | Apply, then re-read what the question asked: encode or decode | Many errors are encode and decode mixed up |
Part 2 — The full menu of coding questions
| Type | What you see | Approach |
|---|---|---|
| Fixed letter shift | CAT = DBU, DOG = ? | Same shift for every letter |
| Alternating shift | LOVE = MNWD | +1, −1, +1, −1 |
| Increasing shift | CODE = DQGI | +1, +2, +3, +4 |
| Mirror (opposite) letters | ROSE = ILHV | 27 − position |
| Reverse the word | LOVE = EVOL | Read backwards |
| Reverse then shift | WORD = ESPX | Two operations in order |
| Position numbers | MAN = 13-1-14 | Replace each letter by its position |
| Sum or product of positions | CAB = 6 | Add (or multiply) positions |
| Message coding | Three coded sentences, find one word's code | Find common words and common codes |
| Substitution | "Red is called blue ..." | Follow the chain literally |
| Symbol coding | FAN = @#& | Match symbols to letters |
| Conditional coding | Vowels become *, consonants shift | Apply the conditions strictly |
| Operation substitution | "+ means ×, × means −" | Swap the signs, then calculate |
| Decoding | Given the code, find the word | Reverse the rule |
Part 3 — Letter-shift codes in depth
A letter-shift code moves every letter along the alphabet by a fixed rule. Compare the first letter of the word with the first letter of the code to find the shift, then check the second letter.
| Code type | Example | Reading |
|---|---|---|
| Fixed shift forward | CAT = DBU | Every letter +1 |
| Fixed shift backward | BUS = ATR | Every letter −1 |
| Alternating | LOVE = MNWD | L+1, O−1, V+1, E−1 |
| Increasing | CODE = DQGI | C+1, O+2, D+3, E+4 |
| Mirror | ROSE = ILHV | R↔I, O↔L, S↔H, E↔V |
| Reverse then shift | WORD = ESPX | Reverse to DROW, then +1 each |
| Wrap-around | ZOO = CRR | Z+3 wraps to C; O+3 is R |
Encode versus decode. When you encode, apply the rule as given. When you decode, apply the inverse. If the code adds 3, decoding subtracts 3. If the code reverses and then adds 1, decoding subtracts 1 and then reverses. Always undo steps in the reverse order from the way they were done.
Pause and predict: In a certain code, ZOO is written CRR. How would FDW be decoded?
Check your answer: Each letter was moved +3 (Z wraps to C, O goes to R). To decode, subtract 3: F becomes C, D becomes A and W becomes T. The word is CAT.
Part 4 — Number codes
Number codes replace letters with numbers, or turn words into totals.
| Code type | Example | Reading |
|---|---|---|
| Position list | MAN = 13-1-14 | M = 13, A = 1, N = 14 |
| Shifted position list | MAN = 14-2-15 | Each letter +1, then positions |
| Sum of positions | CAB = 3 + 1 + 2 = 6 | Add the positions |
| Product of positions | BAD = 2 × 1 × 4 = 8 | Multiply (check which operation the example uses) |
| Reverse position list | MAN = 14-1-13 | Positions written backwards |
| Letter count | TEACHER = 7 | Number of letters |
If one example gives a total (for instance DOG = 26), test the sum of positions first: D (4) + O (15) + G (7) = 26. Then CAT = 3 + 1 + 20 = 24.
Part 5 — Message (sentence) coding
You are given several coded sentences and asked for the code of one word. The trick is the common word: a word that appears in two sentences has a code that appears in both coded sentences.
| Sentence | Code |
|---|---|
| sun shines bright | ka ma ta |
| bright moon night | ta ra sa |
| moon sun rise | ma sa pa |
Sentences 1 and 2 share "bright" and the code ta appears in both, so bright = ta. Sentences 1 and 3 share "sun" and the code ma, so sun = ma. Sentences 2 and 3 share "moon" and sa, so moon = sa. Then the rest follows: shines = ka, night = ra, rise = pa. So the code for "moon" is sa.
Method: (1) find a word that appears in exactly two sentences, (2) find the code that appears in the same two coded sentences, (3) match them, (4) remove them and repeat. Never assume the codes appear in the same order as the words.
Part 6 — Substitution, symbol and conditional codes
Substitution. The sentence redefines words, and you follow the chain, ignoring real meaning. For example: "red is called blue, blue is called green, green is called white, white is called yellow". The colour of grass is green. Green is called white. The answer is white.
Symbol coding. Given FAN = @#& and NAP = &#%, align the letters: F = @, A = #, N = &, P = %. Then PAN = %#&.
Conditional coding. A set of rules is applied in order. Example: replace each vowel by the next letter and each consonant by the previous letter. BEAD becomes B (consonant, previous) = A, E (vowel, next) = F, A = B, D = C, so the code is AFBC.
Operation substitution. The question swaps the meaning of signs. Rewrite the expression with the true signs before calculating.
Part 7 — Worked examples with full reasoning
1. If CAT = DBU, then DOG = ? C (3) to D (4), A (1) to B (2), T (20) to U (21). Each letter is +1. D to E, O to P, G to H. The answer is EPH.
2. If MAN is coded 13-1-14, then SUN = ? The code lists positions: M = 13, A = 1, N = 14. S = 19, U = 21, N = 14. The answer is 19-21-14.
3. Mirror code: ROSE = ? R (18) mirrors to 27 − 18 = 9 = I. O (15) to 12 = L. S (19) to 8 = H. E (5) to 22 = V. The answer is ILHV.
4. LOVE is written MNWD. How is TIME written? L+1 = M, O−1 = N, V+1 = W, E−1 = D, so the shifts alternate +1, −1, +1, −1. TIME: T+1 = U, I−1 = H, M+1 = N, E−1 = D. The answer is UHND.
5. CODE is written DQGI. How is LAMP written? C+1 = D, O+2 = Q, D+3 = G, E+4 = I, so the shifts rise by 1 each time. LAMP: L+1 = M, A+2 = C, M+3 = P, P+4 = T. The answer is MCPT.
6. ZOO is written CRR. Decode FDW. The shift is +3 forward. To decode, subtract 3: F−3 = C, D−3 = A, W−3 = T. The answer is CAT.
7. Message coding (Part 5 table). Find the code for "moon". The common word in sentences 2 and 3 is "moon" and the common code is "sa". The answer is sa.
8. Substitution. If red is called blue, blue is called green, green is called white, white is called yellow and yellow is called black, what is the colour of the sky? The sky is blue. Blue is called green. The answer is green.
9. Sum coding. If DOG = 26, then what is CAT? D (4) + O (15) + G (7) = 26, so the code is the sum of positions. CAT = 3 + 1 + 20 = 24.
10. Reverse then shift. WORD is written ESPX. Reverse WORD to get DROW, then add 1 to each letter: E, S, P, X. Using the same code, how is MAKE written? Reverse to EKAM, then +1: F, L, B, N. The answer is FLBN.
11. Symbol coding. FAN = @#& and NAP = &#%. What is PAN? From the two codes, F = @, A = #, N = &, P = %. So PAN = %#&.
12. Conditional coding. Each vowel is replaced by the next letter in the alphabet and each consonant by the previous letter. What is the code for BEAD? B (consonant) becomes A, E (vowel) becomes F, A (vowel) becomes B, D (consonant) becomes C. The answer is AFBC.
13. Operation substitution. If + means ×, × means −, − means ÷ and ÷ means +, then what is the value of 12 ÷ 4 + 3 × 5 − 5? Translate each sign into its real operation: ÷ becomes +, + becomes ×, × becomes −, − becomes ÷. The expression becomes 12 + 4 × 3 − 5 ÷ 5. Apply BODMAS: 4 × 3 = 12 and 5 ÷ 5 = 1. So 12 + 12 − 1 = 23.
14. Alternating mixed code. In a code, MAN is written as 14-2-15. How is SIT written? Each letter is moved +1 and then written as a position: M to N = 14, A to B = 2, N to O = 15. S to T = 20, I to J = 10, T to U = 21. The answer is 20-10-21.
Part 8 — Common traps
| Trap | Why it is tempting | The truth |
|---|---|---|
| Assuming a forward shift | Most examples go forward | Test backward and the mirror as well |
| Applying the shift once, not on every letter | The first letter looks right | Verify all letters |
| Confusing encode with decode | The question asks for one, you do the other | Re-read the last line of the question |
| Off-by-one in positions | A feels like 0 | A = 1 and Z = 26 |
| Forgetting the wrap-around | You stop at Z | After Z, count from A |
| Mixing sum with list of positions | Both use positions | Check whether the example is a total or a list |
| Using real meaning in substitution | Grass is green in real life | Follow the stated chain only |
| Reversing steps in the wrong order | Two operations in the code | To decode, undo the last step first |
| Wrong BODMAS after swapping signs | You calculate left to right | Swap signs first, then apply BODMAS |
Part 9 — Rapid-fire practice
Write the positions first, then compare your answers with the table.
| No. | Question | Answer | Rule |
|---|---|---|---|
| 1 | If BAT = DCV, how is RAT written? | TCV | +2 each letter |
| 2 | Mirror code: MIND = ? | NRMW | M↔N, I↔R, N↔M, D↔W |
| 3 | Positions of FACE | 6-1-3-5 | Position list |
| 4 | Sum of positions of BEG | 14 | 2 + 5 + 7 |
| 5 | Reverse the word LOVE | EVOL | Reverse |
| 6 | +3 code: HELP = ? | KHOS | H→K, E→H, L→O, P→S |
| 7 | −1 code: BUS = ? | ATR | B→A, U→T, S→R |
| 8 | If cat is called dog, dog is called cow, cow is called goat, which animal gives milk? | goat | Cow gives milk and is called goat |
| 9 | In a +1 code, IBMG is the code of | HALF | I→H, B→A, M→L, G→F |
| 10 | Alternating +1, −1 code: MORE = ? | NNSD | M+1, O−1, R+1, E−1 |
| 11 | If A = 1, then ACE as a sum | 9 | 1 + 3 + 5 |
| 12 | If TEA = 26, then MILK = ? | 45 | 13 + 9 + 12 + 11 |
| 13 | Each letter +1, then written as its position. CAT = ? | 4-2-21 | D, B, U |
| 14 | Replace each vowel by *: EDUCATION | *D*C*T**N | E, U, A, I, O are vowels |
| 15 | If + means −, and − means +, then 15 + 5 − 3 = ? | 13 | 15 − 5 + 3 |
Part 10 — A timed-practice routine
| Day | Task | Target |
|---|---|---|
| 1 | Memorise EJOTY and the mirror rule; write the alphabet with positions from memory | Under 60 seconds |
| 2 | 20 letter-shift codes with positions written | Shift named for every question |
| 3 | 15 number, sum and reverse codes | No mixing of sum and list |
| 4 | 10 message codes, 10 substitution and symbol codes | Method: common word first |
| 5 | 10 conditional and operation-substitution questions | Follow conditions in order |
| 6 | Mixed set of 20 | 15 minutes, about 45 seconds each |
| 7 | Redo wrong ones; timed set of 20; the 30 practice questions attached to this page | 12 minutes |
One-line revision: write letter positions first, test fixed shift, alternating shift and the 27-mirror before anything fancy, follow substitution chains literally, and decode by undoing the steps in reverse order.
Part 11 — Where this connects
Coding-decoding uses the same positions as Number & Letter Series, and its "same rule, new input" thinking is the heart of Analogy. Odd-one-out sets in Classification often test letter positions too. Operation-substitution questions need the order of operations from Arithmetic.
Practice questions
Now test yourself. 8 free sample questions with explanations. 32 more in the timed practice test.
Q1. A word is coded by shifting each letter +1 and reversing the word. By this rule, what is the code for NORTH?
▸ Show answer & explanation
Answer: A
Shift +1: N->O, O->P, R->S, T->U, H->I gives OPSUI. Reversing OPSUI gives IUSPO.
Q2. In a certain code, FLOWER is written as EKNVDQ. How is GARDEN written?
▸ Show answer & explanation
Answer: A
Each letter is shifted -1: F->E, L->K, O->N, W->V, E->D, R->Q. GARDEN: G->F, A->Z, R->Q, D->C, E->D, N->M = FZQCDM.
Q3. If each letter is replaced by its opposite letter in the alphabet (A<->Z), then how is CAT coded?
▸ Show answer & explanation
Answer: A
Opposite = 27 minus position. C(3)->X(24), A(1)->Z(26), T(20)->G(7), giving XZG.
Q4. In a code language, GOLD is written as 7-15-12-4 and SILVER as 19-9-12-22-5-18. Using letter-position coding, how is IRON written?
▸ Show answer & explanation
Answer: A
Each letter equals its alphabet position: I=9, R=18, O=15, N=14, giving 9-18-15-14.
Q5. In a code, each letter is replaced by the one diametrically opposite in the alphabet (A<->Z, B<->Y). How is HELP coded?
▸ Show answer & explanation
Answer: A
Opposite letter = 27 minus position. H(8)->S(19), E(5)->V(22), L(12)->O(15), P(16)->K(11), giving SVOK.
Q6. In a certain code, MANGO is coded as 13-1-14-7-15. How is APPLE coded using the same logic?
▸ Show answer & explanation
Answer: A
Each letter is replaced by its position in the alphabet: A=1, P=16, P=16, L=12, E=5, giving 1-16-16-12-5.
Q7. In a code, PEN is written as 16-5-14 and BOOK as 2-15-15-11. By the same logic, what is the code for DESK?
▸ Show answer & explanation
Answer: A
Each letter equals its alphabet position: D=4, E=5, S=19, K=11, giving 4-5-19-11.
Q8. If LIGHT is coded as JGEFR, how is SOUND coded in the same language?
▸ Show answer & explanation
Answer: A
Each letter shifts -2: L->J, I->G, G->E, H->F, T->R. SOUND: S->Q, O->M, U->S, N->L, D->B = QMSLB.
🔒 32 more questions
Attempt all 40 Coding-Decoding questions in real NTA exam format with timer and instant scoring.
Start practice test →