कोडिंग-डिकोडिंग (उन्नत)

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Coding-Decoding (Advanced)

1. Outline & Learning Goals

By the end of this chapter you will be able to:

1. Identify the type of any coding question within 10 seconds (letter-shift, substitution, number, symbol, mixed, sentence coding, new-pattern).
2. Apply the EJOTY position system to crack letter-shift codes without counting on fingers.
3. Solve matrix coding, symbol coding with conditions, and Chinese-style sentence coding — the three formats that dominate SSC CGL, IBPS PO and RRB NTPC mains-level papers.
4. Spot the examiner's favourite traps: multiple valid relations, reverse-order reading, and "cannot be determined" options.
5. Decide in 5 seconds whether a question is worth attempting or skipping.

2. The Hook: Why This Chapter Decides Your Rank

Coding-decoding appears regularly in SSC CGL and IBPS PO reasoning sections, and these are among the fastest marks in the paper. A trained student solves a coding question in 20–30 seconds; an untrained one burns 3 minutes and still picks the trap option. Over a full paper, saving even a minute on each such question frees up time for the questions that actually decide your score.

The good news: coding-decoding is 100% pattern-based. There is no luck, no general knowledge, no vocabulary. Once you can see the pattern, the answer is mechanical. This chapter trains your eyes to see it.

3. The Common Struggle (and Why It Happens)

Most students fail here for one reason: they start counting letters on their fingers. A → B → C → D… By the time they reach the fourth letter, they have lost the thread.

The fix is simple: memorise letter positions once, forever. Every advanced coding question is just arithmetic on positions 1–26. If you know that M = 13 and N = 14 instantly, half the battle is won before you read the options.

The second struggle: students assume there is only one possible pattern. Advanced questions deliberately offer two plausible patterns, and the examiner puts the wrong one as option (a). We will train you to verify before you commit.

4. The Foundation: Letter Positions and EJOTY

Learn the alphabet positions cold:

A1 B2 C3 D4 E5 F6 G7 H8 I9 J10 K11 L12 M13 N14 O15 P16 Q17 R18 S19 T20 U21 V22 W23 X24 Y25 Z26

Mnemonic — EJOTY: The letters at positions 5, 10, 15, 20, 25 spell E-J-O-T-Y. Remember it as *"EJOTY — Enjoy The Year."* From these five anchors, any letter is at most 2 steps away. Want R? O is 15, so R = 18. Want W? T is 20, Y is 25, so W = 23.

Opposite letters (position from the end = 27 − position): Pairs that sum to 27 —
AZ, BY, CX, DW, EV, FU, GT, HS, IR, JQ, KP, LO, MN.
Mnemonic: *"A-Z, B-Y, C-X, D-W… the alphabet folds in half at M-N."* Advanced questions love opposite-letter coding (e.g., CAT → XZG).

🧠 Active Recall: Without looking up — what is the position of K? What is the opposite of H? What letter is 7th from the end? (Answers: 11, S, T.)

5. Type 1: Letter-Shift Coding (Arithmetic on Positions)

Each letter is shifted by a fixed or varying number.

Example: If DOG is coded as FQI, how is CAT coded?

• D(4)→F(6): +2; O(15)→Q(17): +2; G(7)→I(9): +2. Uniform shift of +2.
• CAT → C+2=E, A+2=C, T+2=V → ECV.

Advanced variant — increasing shift: +1, +2, +3…
Example: If MAN → NCQ, find the rule.

• M+1=N, A+2=C, N+3=Q → shift increases by 1 each letter: +1, +2, +3.

Rule: A pattern must hold for every letter of the given example. If it fails even once, reject it.

🧠 Active Recall: What is the first thing you do when shifts look inconsistent across letters? (Answer: check for reverse order, opposite letters, or a vowel/consonant split.)

6. Type 2: Reverse and Mixed-Order Coding

The examiner's favourite upgrade: shift the letters and write the result in reverse.

Example: If TABLE is coded as GZYOV, how is CHAIR coded?

• T→G: T is 20, G is 7 → 20+7 = 27. Opposite letters! Check: A→Z (1+26=27 ✓), B→Y ✓, L→O ✓, E→V ✓.
• So CHAIR → XSZRI (C→X, H→S, A→Z, I→R, R→I).

Mixed order: Sometimes the word is reversed first, then shifted. The correct approach: test (a) plain shift, (b) shift + reverse, (c) reverse + shift, in that order. One of these three covers most exam questions.

7. Type 3: Number Coding

Letters are replaced by numbers — usually their positions, sometimes with a twist.

Example: If CAT = 3-1-20, then DOG = 4-15-7. (Direct positions.)

Advanced variants:

• Sum coding: CAT = 3+1+20 = 24.
• Product or digit-sum: CAT = 24 → 2+4 = 6.
• Positional squares or multiples: A=2, B=4, C=6… (position × 2).
• Reverse positions: A=26, B=25 … Z=1.

🧠 Active Recall: If SUN is coded by the sum of positions, what is the code? (S=19, U=21, N=14 → 54.) And if digit-summed once more? (5+4 = 9.)

8. Type 4: Symbol Coding with Conditions (Bank-Exam Favourite)

A set of letters/digits is coded as symbols, with conditions that change the rule for specific cases. This is where IBPS and SBI PO separate toppers from the rest.

Model format:
Digits: 1 2 3 4 5 6 7 8 9
Codes: @ # $ % & * ! ? ^

Conditions:
(i) If the first digit is odd and the last digit is even, both are coded as ©.
(ii) If the first digit is even and the last digit is odd, swap the codes of the first and last digits.

Example: Code for 3 5 2 8 4 → first digit 3 (odd), last digit 4 (even) → condition (i) applies → © & # ? ©.

Method: (1) Write the plain code first. (2) Read conditions one by one. (3) Apply only the first condition that matches — conditions are usually mutually exclusive. (4) Never apply two conditions unless the question says so.

Trap: Students apply the condition *and* forget it replaces the original code, or they apply condition (ii) after (i). Read "if… otherwise…" language very carefully.

9. Type 5: Sentence Coding ("Chinese Coding")

Several sentences are given with their codes; you find the code of one word by elimination.

Example:

• "Ram is tall" → "ka ma ta"
• "Shyam is short" → "ma pa ra"
• "Ram is happy" → "ka ma na"

Find the code for "tall":

• "is" appears in all three → common code in all three = ma → is = ma.
• "Ram" appears in sentences 1 and 3 → common code = ka → Ram = ka.
• Therefore in sentence 1, "tall" = ta.

Method: Pick the word asked. Find every sentence containing it. Intersect their codes. If exactly one code is common — done. If two remain, the answer is "either of these" or "cannot be determined" — and examiners do include that option deliberately.

🧠 Active Recall: In the example above, what is the code for "happy"? (Sentence 3: ka=Ram, ma=is, so happy = na.)

10. Type 6: Substitution Coding (Direct Replacement)

A word is simply renamed: "red is called blue, blue is called green, green is called white…"

Example: If red is called blue, blue is called green, and green is called yellow, what is the colour of grass?

• Grass is green → green is called yellow. Answer: yellow.

Trap: Students answer "green" (the real colour) instead of following the chain. The question always asks what it is called, not what it is. Follow the chain exactly one step — or two, if the question nests the substitution ("what is the colour of the sky called in the new code?" — sky is blue, blue is called green → green).

11. Type 7: Matrix Coding

Two matrices give row-column codes for each letter. A letter is identified by (row, column).

Model: Matrix I rows/columns 0–4, Matrix II rows/columns 5–9. Letter A might be represented by 00, 14, 21, 33, 42 (any cell containing A).

Method: For each letter of the word, list all its valid (row, column) pairs from the matrices. Then check which option gives a valid pair for every letter. Eliminate option by option — never try to build the code from scratch.

Trap: An option where 3 of 4 letters are valid but one pair points to the wrong letter. Check every letter, especially the last one — examiners put the error there because tired students stop checking.

12. Type 8: New-Pattern / Conditional Letter Coding (Latest Trend)

Recent SSC and bank papers use rules like: *"Each vowel is replaced by the next letter and each consonant by the previous letter."*

Example: Code for BREAK: B→A (consonant, −1), R→Q, E→F (vowel, +1), A→B, K→J → AQFBJ.

Other live patterns:

• Vowels → their position number; consonants → next letter.
• First half of word shifted +1, second half −1.
• Letters at odd positions +2, even positions −2.

Method: Split the word into the categories the rule names (vowel/consonant, odd/even position, first/second half), apply the rule category by category, then reassemble.

🧠 Active Recall: Using "vowel +1, consonant −1", code the word CODE. (C→B, O→P, D→C, E→F → BPCF.)

13. The Universal 5-Step Solving Algorithm

For any coding question, run this checklist in order:

1. Count letters — same length in word and code? If not, it's sum/substitution type.
2. Check uniform shift — is the gap identical for all letters?
3. Check varying shift — +1/+2/+3, or odd/even position rules.
4. Check reverse/opposite — do positions sum to 27? Is the code the word reversed?
5. Check split rules — vowels vs consonants, halves, swaps.

Most exam questions are cracked by step 4. If nothing fits by step 5, mark for review and move on — it's a deliberately hard question designed to eat your time.

14. Summary Table

⚠️ Caution: Examiner's Trap

Trap 1 — Multiple plausible relations. The example word may fit two patterns (e.g., +2 shift *and* opposite-letter with reversal). The examiner places the answer from the wrong pattern as option (a). Defence: verify your pattern on *every* letter of the example, and if two patterns fit, check which one's answer appears among the options — then re-verify that one.

Trap 2 — Intimidating vocabulary and long words. Words like "PHILANTHROPY" or "ARCHITECTURE" are used to scare you into skipping. The pattern is never harder for a long word — it just takes 10 extra seconds. Defence: never skip a coding question because the word looks big; skip only if the *pattern* doesn't reveal itself in 30 seconds.

Trap 3 — Double-relation and "cannot be determined" questions. In sentence coding, sometimes a word's code cannot be uniquely fixed (two codes remain possible), and "cannot be determined" is a genuine option — not a filler. In symbol coding, two conditions may *seem* to apply, but only the first matching one does. Defence: in sentence coding, if elimination leaves two candidates, choose "cannot be determined" confidently instead of guessing; in conditional coding, re-read whether conditions are exclusive ("if… otherwise") or cumulative.

Review this chapter after 2 days — redo every 🧠 Active Recall prompt from memory and re-solve one example of each type without looking at the solution. Patterns fade fast; two spaced revisions make them permanent.