Coding‑Decoding – Easy Study Notes for Sikkim PSC
1. What is Coding‑Decoding?
- Coding = turning a word into numbers or symbols.
- Decoding = changing the numbers/symbols back into a word.
- Think of it like a secret message: you replace letters with clues that only you know.
2. Everyday Analogy
| Real life | Coding‑Decoding |
|---|---|
| Lock & key | Numbers = lock, letters = key |
| Phone keypad | 2=ABC, 3=DEF, … |
| Secret notes | Replace “A” with “@”, “B” with “#”, etc. |
3. How It Usually Looks
| Code | Decoded Word |
|---|---|
| 1 2 3 | A B C (A=1, B=2, C=3) |
| 5 4 3 | E D C (E=5, D=4, C=3) |
| X Y Z | 24 25 26 (X=24, Y=25, Z=26) |
| 3 3 3 | M M M (M=13, 3rd letter of alphabet) |
Remember: The code can be simple (A=1) or a bit tricky (A=26, B=25 …).
4. Common Patterns
| Pattern | Example | How to Spot It |
|---|---|---|
| Alphabetic order | 1 2 3 4 | Numbers go up by 1. |
| Reverse order | 26 25 24 | Numbers go down by 1. |
| Same number for same letter | 7 7 7 | Repeated number = same letter. |
| Skip by a fixed amount | 1 4 7 10 | Add 3 each time. |
| Mirror of alphabet | 26 25 24 | A=26, B=25, … Z=1. |
| Position in word | 3 1 2 | 3rd, 1st, 2nd letters of a word. |
5. Step‑by‑Step Strategy
- Read the whole clue – see if it gives a hint (e.g., “A=1, B=2…”).
- Look for patterns – check if numbers are increasing, decreasing, or repeating.
- Try the simplest pattern first – alphabetic order or reverse.
- Test with a short word – e.g., “3 1 4” → maybe “C A D”.
- Check the options – if it’s a multiple‑choice test, see which option matches the pattern.
- Confirm – once a word fits, double‑check the whole code.
6. Tiny Example
| Code | Decoded Word |
|---|---|
| 1 5 3 | A E C (A=1, B=2, C=3, …) |
Why it works:
- 1 → A
- 5 → E
- 3 → C
So the word is “AEC”.
7. Sample Question (with Solution)
Question
23 22 21 20 19
Which word does it represent?
Options
A. STUVW
B. PQRST
C. VWXYZ
D. GFEDC
Solution
- Numbers are decreasing by 1.
- 23 → W, 22 → V, 21 → U, 20 → T, 19 → S.
- The word is W V U T S → “WVU TS”.
- Check options → Option A (STUVW) is the reverse of our decoded word, but the order is the same.
- So the correct choice is A.
8. Quick Checklist for Exam Day
- ✅ Read the code carefully.
- ✅ Identify if numbers go up or down.
- ✅ Look for repeats.
- ✅ Try the simplest mapping first.
- ✅ Pick the option that fits the pattern.
- ✅ Double‑check the last letter.
9. Mini Practice Problems
| # | Code | Find the word |
|---|---|---|
| 1 | 1 2 3 | |
| 2 | 26 25 24 | |
| 3 | 3 3 3 | |
| 4 | 5 4 3 2 1 | |
| 5 | 2 6 10 14 |
Hint:
- 1 → A, 2 → B, 3 → C, …
- 26 → Z, 25 → Y, …
10. Final Tips
- Practice with real words – e.g., “HELLO” → 8 5 12 12 15.
- Use a phone’s calculator to add or subtract quickly.
- Keep calm – most codes use a single simple rule.
- Time‑management – spend about 5–7 seconds per question.
Good luck with your Sikkim PSC preparation!