RBI Grade B – Reasoning Ability
Topic: Coding‑Decoding
Coding means turning a word or phrase into a secret message.
Decoding is the opposite – figuring out the original word.
1. Why It Matters
- Many exams ask you to read a coded sentence and pick the correct answer.
- The skill is like a secret decoder ring – once you know the trick, the answer pops out.
2. Everyday Analogy
Think of coding like putting a secret message in a letter box that only the person who knows the key can open.
- Key = the rule that turns letters into numbers or symbols.
- Message = the coded form you see on paper.
3. Common Coding Rules (in plain language)
| Rule | What It Does | Tiny Example |
|---|---|---|
| Alphabet Shift | Move letters forward/backward in the alphabet. | CAT → FDU (C→F, A→D, T→U) |
| Position Swap | Letters change places. | SUN → NUS |
| Number‑Letter Match | Numbers represent letters (A=1, B=2, …). | 3-1-20 → C-A-T |
| Reverse Order | Write the word backward. | DOG → GOD |
| Mixed | Combine two of the above. | BIRD → 2-9-18-4 (B=2, I=9, R=18, D=4) |
Tip: Look at the first pair of coded/decoded words to spot the rule.
4. Step‑by‑Step Decoding Process
- Write down both words side by side.
- Compare letters one by one.
- Notice any pattern – shift, swap, number, reverse, etc.
- Apply the pattern to the next word in the series.
- Check if the answer fits the pattern.
5. Quick Practice Example
| Coded | Decoded |
|---|---|
| 3‑1‑20 | CAT |
Question: If 3‑1‑20 is CAT, what is 4‑15‑7?
Solution Steps
- 4 → D, 15 → O, 7 → G.
- The decoded word is DOG.
Answer: DOG
6. Common Question Types
| Type | What to Do |
|---|---|
| Series | Identify the rule from the first pair, then predict the next. |
| Insertion | Find the missing word that keeps the pattern. |
| Reversal | Spot words written backward. |
| Mixed | Check if two rules are used together. |
7. Quick‑Reference Cheat Sheet
| Rule | Symbol | Example | How to Spot |
|---|---|---|---|
| Alphabet Shift (+1) | → | A → B | Letters move one step forward. |
| Alphabet Shift (−1) | ← | B → A | Letters move one step backward. |
| Swap | ↔ | ABC → BAC | Second letter moves to first. |
| Reverse | ↺ | DOG → GOD | Word read from end to start. |
| Number‑to‑Letter | 1‑26 | 3‑1‑20 → CAT | Numbers match alphabet positions. |
8. Tips for Exam Day
- Read the whole question first – the pattern may involve more than one word.
- Work quickly through the first pair – the rule usually shows up early.
- Don’t overthink – simple shifts or swaps are most common.
- If stuck, try the easiest rule (shift, reverse, number).
- Use elimination – if an answer doesn’t follow the rule, discard it.
9. Mini‑Quiz for Practice
| Coded | Decoded |
|---|---|
| 5‑14‑20 | E‑N‑T |
| 9‑7‑12‑19 | I‑G‑L‑S |
| V‑H‑M | ? |
Answer Key
| Coded | Decoded |
|---|---|
| 5‑14‑20 | ENT |
| 9‑7‑12‑19 | IGLS |
| V‑H‑M | M‑H‑V (reverse) |
10. Final Takeaway
- Coding‑decoding is all about spotting a simple rule.
- Treat it like a secret recipe: find the key, apply it, and the answer is ready.
- Practice a few patterns each day, and you’ll decode any question in no time!
Good luck, and remember: The key is always in the first pair.