TNPSC Group II · Bite-size lessons
Alphanumeric Reasoning
About 6 min · Aptitude and Mental Ability · English
Time worked out from the lesson's 345 words at 150 words a minute, plus a minute for each question.
Alphanumeric reasoning tests your ability to decode patterns involving letters, numbers, and symbols. The questions assess logical thinking and pattern recognition rather than mathematical computation.
Key ideas
- Alphabet Position Values: A=1, B=2, C=3... Z=26. The reverse mapping (A=26, Z=1) is equally common. Memorize both directions.
- Letter Shifting: Moving forward or backward in the alphabet by fixed positions. Example: C (+2) = E, and wrapping occurs at Z (Z+1 = A).
- Coding-Decoding Logic Types: Letter substitution (A→D), number substitution (A→1), reverse order coding, and symbol-based coding.
- Opposite Letters: Letter pairs summing to 27 are opposites. A↔Z, B↔Y, C↔X, D↔W, and so on. Quick formula: Opposite of letter at position n = letter at position (27-n).
- EJOTY Formula: E=5, J=10, O=15, T=20, Y=25. These benchmark positions help calculate nearby letters instantly.
Watch out for
- Forgetting wrap-around at Z: Students calculate X+5 as 29, forgetting to cycle back. Fix: Use modulo 26, so X(24)+5 = C(3), not position 29.
- Confusing forward and reverse positions: Assuming A=1 always, when the code uses A=26. Fix: Always verify the coding direction from the given example before solving.
- Miscounting alphabet positions: Mental errors like thinking M=14 instead of M=13. Fix: Use EJOTY anchors—M is 2 positions before O(15), so M=13. Count carefully or write out nearby letters.
Quick reference
- EJOTY = 5, 10, 15, 20, 25 — memorize as your alphabet calculator
- Opposite pairs sum to 27: A+Z=27, B+Y=27, M+N=27
- Midpoint formula: (Position1 + Position2) ÷ 2
- Always decode the example first before attempting the answer
- In series: separate letter patterns from number patterns — they often follow independent rules
Check yourself: 3 questions
1. If in the English alphabet, every alternate letter starting from B is replaced by the next letter and the remaining letters are replaced by the previous letter, which letter will be the 5th to the right of the 12th letter from the left?
2. In a certain code, 'ROME' is written as '6417' and 'DEAR' is written as '8146'. How is 'MADE' written in that code?
3. Find the missing term in the series: A1B, C3D, E5F, G7H, ?
This lesson is cut from the topic's note, not rewritten. Fact-checked on 17 Oct 2026: an AI-assisted check of this note against cited sources; the errors it found were corrected that day. Some errors may remain. The questions are from Shishya's validated question bank.
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