Coding‑Decoding – SBI Clerk (Reasoning Ability)
Coding‑Decoding is a common question type in the SBI Clerk exam where you are required to convert a given pattern of numbers, letters or symbols into another form (or vice‑versa).
It tests your ability to spot hidden relationships, recognise patterns and apply logical reasoning.
1. Simple Explanation
- Coding: Convert a word/phrase into a series of numbers or symbols according to a rule.
- Decoding: Convert a series of numbers or symbols back into a word/phrase according to the same rule.
The rule is usually consistent within a set and may involve:
- Position of letters in the alphabet
- Alternating patterns (odd/even positions)
- Arithmetic operations (addition, subtraction, multiplication, division)
- Roman numerals, Morse code, binary, etc.
2. Key Points to Remember
| # | Point | Why It Matters |
|---|---|---|
| 1 | Identify the pattern type – alphabetical, numerical, positional, or mixed. | Determines the decoding strategy. |
| 2 | Look for simple arithmetic – e.g., A=1, B=2, C=3, or A=26, B=25 … | Most exam problems use simple math. |
| 3 | Check for alternating patterns – odd positions vs even positions may follow different rules. | Avoids mis‑decoding entire string. |
| 4 | Use the given examples – derive the rule from the given coded/decoded pairs. | Provides concrete evidence of the rule. |
| 5 | Verify consistency – test the rule on all given pairs; if a pair fails, reconsider. | Ensures no mis‑interpretation. |
| 6 | Think of common mapping tricks – e.g., 1=Z, 2=Y, 3=X, etc.; 1=A, 2=B but skip vowels; 1=1st letter, 2=2nd, etc. | Saves time during the exam. |
| 7 | Keep a quick reference table for common coding schemes (alphabet positions, inverse alphabet, etc.). | Reduces mental effort. |
3. Common Coding‑Decoding Schemes in SBI Clerk
| Scheme | Example | How to Decode |
|---|---|---|
| Alphabetic Position | B → 2 |
Number → Alphabet by 1‑based index |
| Reverse Alphabetic | Y → 2 |
Number → 27 – Alphabet index |
| Odd/Even Alternation | A C E G → 1 3 5 7 |
Separate odd and even positions |
| Skip Vowels | B C D F → 2 3 4 6 |
Map only consonants |
| Multiplication/Division | C → 9 (3×3) |
Number → Number/Pattern |
| Binary/Octal | 1011 → K |
Convert binary to decimal then alphabet |
| Morse Code | .- → A |
Translate Morse to letters |
| Pattern in Words | HAPPY → 8 1 16 16 25 |
Use alphabetical positions |
4. Worked Example (Full Step‑by‑Step)
Problem
Given:
B D F→2 4 6E G I→5 7 9
Question: Decode the sequence1 3 5into letters.
Solution
| Step | Action | Reason |
|---|---|---|
| 1 | Observe the pattern | B=2, D=4, F=6 – each letter’s alphabetical position equals the number. |
| 2 | Confirm with second pair | E=5, G=7, I=9 – confirms the rule. |
| 3 | Apply rule to the query | The numbers are 1, 3, 5. Convert each to the 1‑based alphabet position. |
| 4 | Convert | 1 → A, 3 → C, 5 → E. |
| 5 | Result | A C E |
Quick Check
A=1,C=3,E=5– matches the numbers, so the decoding is correct.
5. Quick Revision Summary
- Coding‑Decoding = Translating between letters and numbers/symbols using a hidden rule.
- Identify the rule from given examples.
- Common rules: alphabet position, reversed alphabet, skip vowels, odd/even separation, simple arithmetic.
- Verify each derived rule against all given pairs – consistency is key.
- Decode/Encode by applying the rule systematically.
- Practice with different patterns to become comfortable spotting the logic quickly.
Tip: Keep a small cheat‑sheet of the most frequent mappings (A=1, Z=26, etc.) to speed up during the exam.
Good luck with your preparation!