Coding-decoding: Reasoning Ability Notes for Odisha Police Sub-Inspector (SI)

Coding‑Decoding – Study Notes

Odisha Police Sub‑Inspector (SI) – Reasoning Ability

1. Simple Explanation

Coding – the process of converting a given set of symbols (letters, numbers, shapes, etc.) into another set using a rule or a pattern.
Decoding – the reverse process: finding the original symbols from the coded ones.

In exam questions you are asked to:

Find the rule that generates the coded sequence.
Use that rule to encode a new set or decode a given coded value.

2. Key Points & Strategies

#	What to look for	Typical pattern	How to test it
1	Positional shift	`A → 1, B → 2 …` or `A → 27, B → 28`	Replace letters with numbers and check the arithmetic progression.
2	Arithmetic progression	`1, 4, 7, 10 …`	Compute differences between consecutive terms.
3	Geometric progression	`2, 4, 8, 16 …`	Divide consecutive terms; ratio should be constant.
4	Reverse or Mirror	`1 2 3 4 → 4 3 2 1`	Reverse the order of the sequence.
5	Skipping / Alternate	`1,3,5,7 …`	Check the difference; look for odd/even pattern.
6	Combination of operations	`A + 3, B – 1, C + 5 …`	Apply operations on each element.
7	Alphabetic relation	`A=1, B=2 …` or `Z=1`	Translate letters to numbers or vice‑versa.
8	Grouping & Sub‑grouping	`AB → 12, CD → 34`	Split into groups, use separate rules per group.
9	Pattern in shapes or symbols	`▲ → 3, ■ → 4`	Count sides, vertices, or apply known shape codes.
10	Contextual/Word‑based	“SUN = 15, MOON = 12”	Look for letter count, alphabetical order, etc.

General Approach

Write down the given data clearly.
Look for obvious patterns – arithmetic, geometric, alphabetical, etc.
Test a hypothesis on at least two terms.
Confirm with the remaining terms.
Apply the rule to encode/decode the requested value.
Check the answer against any “unreasonable” result.

3. Worked Example

Question
In the coding system below, each pair “X Y” stands for a two‑digit number.
A 1 = 12  
B 2 = 23  
C 3 = 34  
D 4 = ?
Find the code for D 4.

Step‑by‑Step Solution

Letter	Number	Code	Observation
A	1	12	1 + 1 = 2
B	2	23	2 + 1 = 3
C	3	34	3 + 1 = 4

Rule: The code for “X Y” is simply the concatenation of Y followed by Y+1.

So for D 4:
Y = 4 → Y+1 = 5 → Code = 45.

Answer: 45.

Another Example (Decoding)

Question
The following coding uses the rule “multiply the alphabetic position by 3, then add the position of the second letter.”
4B = 32
5C = 52
6D = ?
Decode the value for 6D.

Step 1 – Decode the given pairs

Input	Alphabetic Position of First Letter	Alphabetic Position of Second Letter	Code
4B	2 (B)	4	4 × 3 + 4 = 16
5C	3 (C)	5	5 × 3 + 5 = 20

Step 2 – Find the rule

The pattern is:

Code = (Position of first letter × 3) + Position of second letter

Step 3 – Apply to 6D

Position of D = 4
Code = 6 × 3 + 4 = 18 + 4 = 22

Answer: 22.

4. Quick Revision Summary

Always write the data clearly – use a table if needed.
Identify the type of pattern early: arithmetic, geometric, alphabetic, positional, reverse, grouping.
Test your hypothesis on at least two terms; confirm with the rest.
Remember common tricks:
- A=1, B=2 … or Z=1
- Shift by a constant (±k)
- Reverse order
- Alternate operations (add, subtract, multiply, divide)
- Concatenation of numbers/letters
Work on time management:
- Spend ≤ 1–2