Coding‑Decoding – Quick Study Notes (Jharkhand TET – Reasoning Ability)
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| Simple Explanation | Coding and decoding are pattern‑finding tasks where a set of symbols (letters, numbers, shapes, or words) are coded into another form. The test‑taker must identify the rule that transforms the code into the decoded (original) sequence or vice‑versa. |
| Key Points | • Identify the pattern – look for relationships between adjacent elements: arithmetic progression, geometric progression, alphabetical order, positional value, frequency, etc. • Check for multiple rules – often a combination of rules is used (e.g., alternating addition/subtraction). • Work in both directions – if the question gives the coded form, decode it; if it gives the decoded form, code it. • Look for symmetry or mirror patterns – e.g., “A B C” → “C B A”. • Use elimination – if a proposed rule fails for any single pair, discard it. • Practice speed – many questions are timed; being able to spot the rule quickly is essential. |
| Worked Example | Question: Decode the following sequence: Code: 13 15 16 7 5 8 9 5 4 Decoded (original) sequence: ? Answer: S O P F E H I E C (in letters) Solution Steps: 1. Notice the set of numbers: 13, 15, 16, 7, 5, 8, 9, 5, 4. 2. Convert each number to its corresponding letter in the alphabet (1=A, 2=B, …, 26=Z). - 13 → M - 15 → O - 16 → P - 7 → G - 5 → E - 8 → H - 9 → I - 5 → E - 4 → D 3. Find a pattern among the letters – the sequence of letters “MOPGEHIED” does not look meaningful. 4. Check for a second rule – the difference between consecutive numbers: 13→15 (+2), 15→16 (+1), 16→7 (–9), 7→5 (–2), 5→8 (+3), 8→9 (+1), 9→5 (–4), 5→4 (–1). The pattern “+2, +1, –9, –2, +3, +1, –4, –1” is symmetrical: +2, +1, –9, –2 |
| Quick Revision Summary | 1. Identify the basic rule (alphabetic conversion, arithmetic progression, geometric progression, positional shift). 2. Verify the rule with all pairs – if any pair does not fit, try a new rule. 3. Check for composite rules – sometimes two or more operations are applied alternately. 4. Decode or encode as required – practice both directions. 5. Practice with sample sets – use flashcards, online quizzes, or past TET papers. 6. Keep a cheat sheet of common patterns (e.g., “+2, +1, –9…”, “mirror”, “skip‑one”). 7. Time yourself – aim to decode/encode each question in 10–12 seconds. |
Pro Tip: Always write down the first few elements of the sequence and check if they follow a simple arithmetic or geometric rule. If not, test for letter‑number mapping or positional symmetry. Once you spot the rule, the rest usually follows automatically.