Coding-decoding: Reasoning Ability Notes for Assam Patwari / Lekhpal

Coding‑Decoding – Reasoning Ability

(For Assam Patwari / Lekhpal Examination)

1️⃣ Simple Explanation

Coding‑decoding is a reasoning‑based question type in which you are given a code (a set of letters, numbers, symbols, or words) and a decoded (the actual meaning or value).
The task is to:

Decipher the code (find the rule that maps code → decoded).
Use the rule to decode a new code or encode a given decoded item.

Typical formats:

Format	What you’re given	What you must find
1	Code → Decoded	Decoded → Code
2	Code → Decoded	Next Code in sequence
3	Two decoded items → Their codes	Code for a third decoded item

The key is to identify a consistent pattern (alphabetical shift, number association, word relation, etc.).

2️⃣ Key Points to Remember

#	Point	Why It Matters
1	Look for common transformations – shift in alphabets (A→D), numeric pattern (1→3, 2→5), or positional mapping (first letter → last letter).	Most codes are simple substitutions; spotting them quickly saves time.
2	Check the length of code vs decoded. Equal length often means one‑to‑one mapping.	Helps decide whether to use direct substitution or a more complex rule.
3	Identify repeated patterns – same letter in code appears at same position in decoded.	Confirms a consistent rule.
4	Consider mathematical operations – addition, subtraction, multiplication, division on numbers.	Codes involving numbers often use arithmetic.
5	Use the “reverse” method – if you can decode the question’s code, you can often deduce the rule, then apply it to other parts.	Reverse‑engineering is a fast way to discover the rule.
6	Write it down – draw a small table mapping code ➜ decoded.	Reduces mental clutter and prevents mistakes.
7	Practice with word‑based codes – sometimes the code is a synonym, antonym, or a keyword.	Word‑based codes appear frequently in reasoning papers.
8	Time‑management – spend 1–2 minutes on pattern recognition; if stuck, skip and return.	Avoids getting trapped early.

3️⃣ Worked Example

Given
A  →  1  
B  →  4  
C  →  9  
D  →  16  
E  →  25
Question
What is the code for F?

Step‑by‑Step Solution

Observe the pattern
- 1, 4, 9, 16, 25 → These are perfect squares: (1^2, 2^2, 3^2, 4^2, 5^2).
- The letters A, B, C, D, E correspond to the 1st, 2nd, 3rd, 4th, 5th letters of the alphabet.
Deduce the rule
- Rule: Code for the (n^{th}) letter = (n^2).
Apply the rule to the next letter
- F is the 6th letter → (6^2 = 36).
Answer
- F → 36

4️⃣ Another Example – Word‑Based Coding

Given
1. DOVE  →  2  
2. DUCK  →  3  
3. CHEESE  →  5  
Question
What is the code for MOUSE?

Solution

Word	# of vowels	# of consonants	Code
DOVE	2 (O, E)	2 (D, V)	2
DUCK	1 (U)	3 (D, C, K)	3
CHEESE	3 (E, E, E)	3 (C, H, S)	5

Notice: Code = (Number of vowels) + (Number of consonants)
- DOVE: 2+2 = 4 (but code given is 2 → not matching)
- Wait, maybe Code = # of consonants?
- DUCK: 3 consonants → 3 (matches).
- CHEESE: 3 consonants → 3 (does not match 5).

Try another possibility: Code = # of distinct letters

DOVE → distinct letters = 4 → code 2 (no).

Let's attempt Code = Sum of letter positions in alphabet (A=1, B=2, …)

D(4)+O(15)+V(22)+E(5) = 46 → not 2.

We suspect the pattern might be # of letters

DOVE (4 letters) → 2 (maybe 4/2)
DUCK (4 letters) → 3 (4-1)
CHEESE (6 letters) → 5 (6-1)

Better: Code = (# of letters) – 2

DOVE: 4-2=2 ✔
DUCK: 4-1=3 (not consistent).

Let’s try Code = (# of letters) – (# of vowels)

DOVE: 4-2=2 ✔
DUCK: 4-1=3 ✔
CHEESE: 6-3=3 (not 5).

The pattern is actually # of letters – (# of consonants)

DOVE: 4-2=2 ✔
DUCK: 4-3=1 (not 3).

Observation: Perhaps the code is # of letters + (# of vowels)

DOVE: 4+2=6 (no).

Given the confusion, let's simplify the example to a clear pattern.

Revised Example