Coding-decoding: Reasoning Ability Notes for Telangana TET (Teacher Eligibility)

Coding‑Decoding – Reasoning Ability

(Telangana TET – Teacher Eligibility Test)

Coding‑Decoding is a popular sub‑section in reasoning exams where a set of symbols (or letters, numbers, shapes) represents a word or phrase.
The test taker must find the correct mapping (the code) and then decode or encode new words.

1. Simple Explanation

Term	What it means
Code (or Cipher)	A fixed set of rules that replace each element of a word with another element.
Decode	Apply the inverse of the code to convert a coded word back to its plain form.
Encode	Convert a plain word into its coded form using the given code.

Example
If the code is:

A → X ,  B → Y ,  C → Z

then:

Encode "ABC" → "XYZ"
Decode "XYZ" → "ABC"

In TET, the code may involve shifts, reversals, substitutions, mathematical operations, or pattern‑based mapping (e.g., “first letter → last letter”).

2. Key Points to Remember

#	Key Point	Why It Helps
1. Identify the code type	Shift, substitution, reversal, position‑based, numeric, or composite.	Determines the decoding strategy.
2. Look for patterns in given pairs	Compare coded vs. plain pairs to spot regularities.	Saves time; prevents trial‑and‑error.
3. Check for one‑to‑one mapping	Each symbol should map to exactly one counterpart.	Guarantees unique decoding.
4. Use positional clues	First letter ↔ last letter, middle letter ↔ second last, etc.	Useful in reversal or mirror codes.
5. Apply mathematical operations	Addition/subtraction of alphabets, factorial, prime positions.	Handles numeric‑based codes.
6. Verify with multiple pairs	Cross‑check mapping on all given examples.	Ensures consistency.
7. Remember common TET patterns	• Shift by +3 (A→D) • Reverse order • First letter becomes last, second becomes second last, etc.	Saves mental effort.
8. Practice speed	Time limit is 1 hr 30 min, so quick pattern recognition is vital.	Improves accuracy under pressure.

3. Worked Example

Problem

You are given the following coded–plain pairs:

Coded	Plain
M	A
N	B
O	C
P	D
Q	E

Using this code, decode the word “RSP”.

Step‑by‑Step Solution

Identify the Code Pattern
- Observe that each coded letter is three positions ahead of its plain counterpart in the alphabet.
- Example: A (1st) → M (13th). Difference: 13 – 1 = 12.
- But for simpler pattern: Plain → Coded is a shift +12 (or equivalently, Coded → Plain is a shift –12).
Plain Coded Shift (Plain→Coded)

A M +12

B N +12

C O +12

D P +12

E Q +12
Apply the Code to the Word RSP
- Break the word into letters: R, S, P.
- Use the inverse shift (–12) to find the plain letters.
- Alphabet positions:
  - R = 18 → 18 – 12 = 6 → F
  - S = 19 → 19 – 12 = 7 → G
  - P = 16 → 16 – 12 = 4 → D
Result
- The decoded word is “FGD”.

Plain	Coded	Shift (Plain→Coded)
A	M	+12
B	N	+12
C	O	+12
D	P	+12
E	Q	+12

4. Quick Revision Summary

Topic	What to Remember
Definition	Code = mapping rule; Decode = reverse mapping.
Common Patterns	Shift, Reverse, Positional, Numeric.
Strategy	1. Spot the pattern from given pairs. 2. Verify with all pairs. 3. Apply the rule to new words.
Tips	• Always check if mapping is one‑to‑one. • Use alphabet positions to detect shifts. • Look for mirror or reversal patterns.
Practice	Solve at least 10 coding‑decoding problems each week.

Pro‑Tip:
In TET, the code is usually simple (shift or reverse). If you’re unsure, try both on the first few pairs; the correct one will reveal itself quickly.

Final Thought

Coding‑decoding tests your ability to identify patterns, apply logical rules, and execute them quickly. Master the basic strategies above, practice with varied examples, and you’ll ace this section of the Telangana TET!