Coding-Decoding
Coding-decoding for CGPSC CSAT: letter positions, EJOTY, reverse-alphabet pairs, shift and mixed codes, sentence codes and substitution with drills.
Prerequisites
- The English alphabet forwards and backwards, without singing it from A each time.
- Simple addition and subtraction up to 26 — the letter-position arithmetic in this page.
- Syllogisms comes before this page in the chapter; the habit of using only the given information applies here too (see the sentence-code section).
The Hook: The Chit Passed Under the Desk
In a Class X classroom in Jagdalpur, a chit travels from bench to bench: “NFFU BU UIF DBOUFFO”. The teacher confiscates it and cannot read it. The students can — each letter has simply been moved one step forward in the alphabet. Shift every letter one step back and it reads “MEET AT THE CANTEEN”.
That is a code (कूट). Whoever wrote it used one rule, applied it to every letter, and anyone who finds the rule can read every message written with it.
The question this page answers: given a word and its code, how do you find the rule in seconds — and apply it to a new word before the clock runs out?
Why it matters for CGPSC: coding-decoding (कूटलेखन-कूटवाचन) is among the quickest question types in a reasoning section once you know the alphabet positions by heart, and among the slowest if you count on your fingers. Almost all the speed comes from the table below.
The Alphabet You Must Know Cold
| Letter | Position | Reverse partner | Partner’s position |
|---|---|---|---|
| A | 1 | Z | 26 |
| B | 2 | Y | 25 |
| C | 3 | X | 24 |
| D | 4 | W | 23 |
| E | 5 | V | 22 |
| F | 6 | U | 21 |
| G | 7 | T | 20 |
| H | 8 | S | 19 |
| I | 9 | R | 18 |
| J | 10 | Q | 17 |
| K | 11 | P | 16 |
| L | 12 | O | 15 |
| M | 13 | N | 14 |
Two facts make this table quick to rebuild in the exam hall:
$$\boxed{\text{Position of a letter} + \text{position of its reverse partner} = 27}$$$$\boxed{\text{Reverse position of a letter} = 27 - \text{its position}}$$The Main Types of Code
| Type | Rule | Example |
|---|---|---|
| Letter shift | Every letter moves the same number of steps | +1: CAT → DBU |
| Varying shift | Steps follow a pattern (+1, −1, +1 … or +1, +2, +3 …) | +1/−1: BHILAI → CGJKBH |
| Reverse alphabet | Each letter replaced by its partner (A ↔ Z) | BASTAR → YZHGZI |
| Reverse order | The word is written backwards | MAHANADI → IDANAHAM |
| Mixed | Two rules combined (reverse, then shift) | SUKMA → AMKUS → BNLVT |
| Letter to number | Letters replaced by positions, sums or products | CAT → 3-1-20, or sum 24 |
| Sentence (word) code | Each word has a code word; compare sentences | “paddy is green” → “ta ki mo” |
| Substitution | Objects are given false names | “rice” is called “wheat” … |
How to Find the Rule
Write the word and its code one above the other and find the difference in position for each letter.
If RAIPUR is coded as SBJQVS, how is DURG coded?
R→S, A→B, I→J, P→Q, U→V, R→S: every letter moves +1.
DURG → EVSH.
If BASTAR is coded as YZHGZI, how is KORBA coded?
B(2)→Y(25), A(1)→Z(26), S(19)→H(8): each pair adds to 27, so each letter is replaced by its reverse partner.
K→P, O→L, R→I, B→Y, A→Z. KORBA → PLIYZ.
If CAT = 24, what is DOG?
C + A + T = 3 + 1 + 20 = 24: the code is the sum of positions.
D + O + G = 4 + 15 + 7 = 26.
If MAHANADI is written as IDANAHAM, how is INDRAVATI written?
The word is simply reversed: ITAVARDNI. Always check for reversal before looking for shifts — a reversed word looks like a random shift until you read it backwards.
Sentence (Word) Codes
Each word in a sentence has one code word, but the codes are jumbled. Compare two sentences: the word they share has the code they share.
In a code language:
- “paddy is green” is written as “ta ki mo”
- “green field is wide” is written as “mo pu ki ze”
- “wide river” is written as “ze na”
What is the code for “field”?
Sentences 1 and 2 share “is” and “green”, and share the codes “ki” and “mo”. Sentences 2 and 3 share “wide” and the code “ze”. So in sentence 2, the only word left — “field” — must be the only code left: pu.
Similarly “river” = na and “paddy” = ta. But “is” and “green” are “ki” and “mo” in some order — which is which cannot be determined. Options often include exactly that choice.
Substitution Codes
Objects are renamed, and the question asks for a real-world fact in the new names. Find the real answer first, then translate it.
If “pen” is called “book”, “book” is called “bag”, “bag” is called “chalk” and “chalk” is called “board”, what does a teacher write with on a blackboard?
The real answer is chalk. Chalk is called “board” — that is the answer.
Memory Tricks
- EJOTY = 5, 10, 15, 20, 25. E is 5th, J 10th, O 15th, T 20th, Y 25th. Every other letter is at most two steps from one of these anchors: R = T − 2 = 18.
- Partners add to 27. Never memorise “reverse positions” separately; subtract from 27.
- Partner pairs as words: BY, DW (dew), EV (Eve), GT (GT road), HS (high school), IR (Indian Railways), KP, LO, MN (man). With AZ, CX, FU and JQ that is all thirteen pairs.
- M and N split the alphabet — M is 13th, N 14th. Letters A–M are in the first half; their partners are in the second half.
- Check the order: reverse first, then shift. If the code letters look unrelated to the word in place, read the code backwards.
Don’t Confuse
| This | vs | That |
|---|---|---|
| Reverse alphabet — each letter becomes its partner (A ↔ Z) | Reverse order — same letters, written backwards | |
| Position of R = 18 | Reverse position of R = 9 (27 − 18) | |
| Shift +1 from Z wraps to A | Shift −1 from A wraps to Z | |
| Sentence code: word found uniquely | Two shared words with two shared codes — cannot be determined which is which |
Common Mistakes
Practice
Level 1: Foundation
- What is the position of the letter W?
- What is the reverse-alphabet partner of the letter G?
- If PEN is written as QFO, how is INK written?
- If CAT = 24 (sum of positions), what is BAT?
- Which letter is 4th to the right of the 10th letter from the left of the alphabet?
Answers
- 23 (Y is 25, so W = 25 − 2).
- T (G = 7, partner = 27 − 7 = 20 = T).
- JOL (each letter +1).
- 23 (2 + 1 + 20).
- N (10 + 4 = 14th letter).
Level 2: Prelims MCQs
Q1. In a certain code, BHILAI is written as CGJKBH. How is KANKER written in that code?
(a) LZOJFQ (b) LBOLFS (c) JZMJDQ (d) LZOLFQ
Answer: (a) LZOJFQ
B→C (+1), H→G (−1), I→J (+1), L→K (−1), A→B (+1), I→H (−1): the shifts alternate +1, −1.
K+1 = L, A−1 = Z (wrap-around), N+1 = O, K−1 = J, E+1 = F, R−1 = Q → LZOJFQ.
Option (b) applies +1 to every letter and (c) applies −1 to every letter — Trap 1.
Q2. In a code, each letter is replaced by its position counted from Z (that is, Z = 1, Y = 2 … A = 26). If GOLD is written as 20 12 15 23, how is IRON written?
(a) 18 9 12 13 (b) 9 18 15 14 (c) 18 9 13 12 (d) 17 8 12 13
Answer: (a) 18 9 12 13
Reverse position = 27 − position. I = 9 → 18; R = 18 → 9; O = 15 → 12; N = 14 → 13.
Check with GOLD: G = 7 → 20, O = 15 → 12, L = 12 → 15, D = 4 → 23. Option (b) gives the forward positions.
Q3. In a code language:
- “rain brings good crops” is written as “lo mi ta su”
- “good crops need water” is written as “ta su ve ra”
- “water and rain” is written as “ra pi lo”
Consider the following statements:
- The code for “rain” is “lo”.
- The code for “need” is “ve”.
- The code for “crops” is “su”.
Which of the statements given above is/are correct?
(a) 1 only (b) 1 and 2 only (c) 2 and 3 only (d) 1, 2 and 3
Answer: (b) 1 and 2 only
Q4. If “rice” is called “wheat”, “wheat” is called “maize”, “maize” is called “gram” and “gram” is called “mustard”, which is the main crop of Chhattisgarh, the state known as the “rice bowl” (धान का कटोरा)?
(a) rice (b) wheat (c) maize (d) gram
Answer: (b) wheat
Q5. Match each letter in List I with its reverse-alphabet partner (A ↔ Z, B ↔ Y …) in List II:
| List I | List II |
|---|---|
| A. D | 1. N |
| B. H | 2. P |
| C. K | 3. W |
| D. M | 4. S |
(a) A-3, B-4, C-2, D-1 (b) A-3, B-2, C-4, D-1 (c) A-1, B-4, C-2, D-3 (d) A-3, B-4, C-1, D-2
Answer: (a) A-3, B-4, C-2, D-1
Level 3: Speed Drill — Solve in 60 Seconds
Time yourself: each item should take under 60 seconds. In Mains Paper IV (GS-II), write the rule you found (“each letter +1”, “reverse partner”) as your working.
- What is the position of the letter Q?
- If SUKMA is written as BNLVT, how is KORBA written?
- If ZEBRA is written as 26 5 2 18 1, how is CAB written?
- What is the reverse partner of the 20th letter of the alphabet?
- If FISH is written as EHRG, how is POND written?
- If “sky” is called “sea”, “sea” is called “earth” and “earth” is called “sky”, where do people build houses?
Answers with the rule used
- 17 — T is 20 (EJOTY), so Q = 20 − 3.
- BCSPL — SUKMA reversed is AMKUS; each letter +1 gives BNLVT. KORBA reversed is ABROK; +1 gives BCSPL.
- 3 1 2 — letters replaced by positions.
- G — the 20th letter is T; 27 − 20 = 7 = G.
- ONMC — each letter −1.
- “sky” — houses are built on earth, and earth is called “sky”.
Quick Revision Table
| Idea | Rule / Fact |
|---|---|
| Anchors | EJOTY = 5, 10, 15, 20, 25 |
| Reverse partner | Positions add to 27 |
| Reverse position | 27 − position |
| Alphabet halves | A–M (1–13), N–Z (14–26) |
| Shift codes | Check every letter; shifts may alternate or grow |
| Wrap-around | After Z comes A |
| Sentence code | Shared words ↔ shared codes; two shared words → order undetermined |
| Substitution | Find the real answer, then give its code name |
Key Takeaways
- Know every letter’s position and reverse partner instantly — EJOTY and “add to 27” rebuild the table in seconds.
- Find the rule by writing word and code one above the other and checking the shift for every letter.
- Test for reversal (of the word or of the alphabet) before hunting for complicated shifts.
- In sentence codes, match shared words to shared codes; if two words share two codes, their individual codes cannot be determined.
- In substitution codes, the answer is the code name, never the real word.
What’s Next
- Blood Relations — the next topic, including coded relations that combine this page with family trees.
- General Mental Ability — letter and number series use the same alphabet arithmetic.
- Syllogisms — revisit the “only what is given” discipline.
- Logical Reasoning — Quick Revision — every rule from this chapter on one page.