Coding Master - Quick Revision
(for RRB NTPC/Group-D/Alp & other Railway exams)
One-Liners (20)
- A→1, B→2 … Z→26 – keep at fingertips for forward/backward jumps.
- Opposite of A is Z (1+26=27) – use “27-rule” for mirror codes.
- Reverse of a word means reverse of every letter’s number.
- +1, –1, ×2, ÷2 are the four most used “operation chains”.
- In “SENT → +1 each” code, SENT = TFOU; remember to wrap after Z→A.
- “GIFT → HJSU” is +1, +2, +3, +4 pattern – watch increasing steps.
- Vowel→Consonant swap codes: A↔B, E↔C, I↔D, O↔F, U↔G (popular in sets).
- Number coding: pick last letter’s alphabet value as the digit (CAT → 20).
- If “A=%, B=@ …” – always draw the 5-symbol × 5-letter grid first.
- Conditional: “If 1st letter vowel → +2, else –1” – apply BEFORE reversing.
- “SISTER written as 20-10-20-21-6-19” – place value keeps 2-digit format.
- In “reverse + forward” mix, treat halves separately (PRACTICE → ECITCAR + EP).
- For matrix codes, row = (pos – 1) ÷ 5; column = remainder (0→5).
- In digit-letter blends, odd digit → skip 1 letter, even digit → skip 2 letters.
- “SUM of code values” questions – add first, then check divisibility by 3/5.
- If code contains only 3 symbols repeating, suspect triplet (A→#, E→#, I→#).
- Last-letter-first-letter link: code of last letter becomes first number of next word.
- “Shift by prime” codes: 2, 3, 5, 7… – list primes ≤26 once.
- Mirror pair check: A-Z, B-Y… (13 pairs) – saves 50 % time.
- Always verify the decoded word in the answer options – eliminates 3 choices fast.
Formulas/Rules
| Formula / Rule | Use-case |
|---|---|
| 27 – pos = opposite letter | Instant mirror coding |
| (pos ± n) mod 26 → if 0 then 26 | Wrap-around for ± shifts |
| Row = ⌈pos / 5⌉, Col = (pos–1) mod 5 + 1 | 5×5 matrix coding |
| Sum of 1st & last letter codes = middle letter code | Check middle-letter pattern |
| Vowel set {A,E,I,O,U} = {1,5,9,15,21} | Quick vowel spotting |
| Prime positions: 2,3,5,7,11,13,17,19,23 | Prime-shift coding |
| Even-pos letters ×2 → digit; odd-pos ÷2 → digit | Even-odd split coding |
| Reverse(pos) = 27 – pos | Reverse alphabet value |
| Coded digit → letter: 1=A, 2=B…9=I, 0=Z (wrap) | Phone-pad style |
| First-letter code + Last-letter code = constant (k) | k-rule for 3-word sets |
Memory Tricks (Mnemonics)
- AZ-27: “A-Z is 27” – think of an auto-rickshaw number to recall mirror sum.
- Vowels 1-5-9-15-21: “An Eagle Is On Umbrella” – initials & numbers rise.
- 5×5 Matrix: “Five friends in five rows” – forces you to draw grid quickly.
- Shift Primes: “Two Three Five Seven – Two Thumbs For Victory” (2-3-5-7).
- Wrap-around: “After Z comes A – like Monday after Sunday” – never forget mod-26.
Common Errors
| Typical Error | Correct Approach |
|---|---|
| Forgetting to wrap Z+1→A | Always apply mod-26; if 0 treat as 26 |
| Mixing reverse then shift vs shift then reverse | Follow question sequence strictly |
| Counting 26 as remainder 0 | Remainder 0 means 26th letter (Z) |
| Using A=0 instead of A=1 | Railway standards use A=1; confirm once |
| Ignoring double-letter codes (e.g., CH, SH) | Check if digraphs are given special symbols |
5 Quick MCQs
Q1. If “ROSE” is coded as “58” then “LOTUS” is
A) 60 B) 65 C) 70 D) 75
Q2. In a certain code “DELHI” is written as “CDKGH”. Which word is coded as “BCKGP”?
A) CALIF B) CAMEL C) CABLE D) CADET
Q3. If A=#, B=@, C=%, D=$ and so on, the code for “BAD” is
A) @#$ B) @#% C) @%$ D) @$#
Q4. “TEACH” → “HDIZX” by mirror coding. What is “EXAM”?
A) VCZN B) VCZO C) VCZN D) VEZO
Q5. Following the pattern 2, 5, 10, 17, 26, … which letter corresponds to the 6th term?
A) Q B) R C) S D) T
(Answers: 1-B, 2-C, 3-A, 4-A, 5-D)
BETA
