UPSSSC PET · Bite-size lessons

Coding-Decoding

About 7 min · Logic & Reasoning · English

Time worked out from the lesson's 485 words at 150 words a minute, plus a minute for each question.

These questions test your ability to identify patterns in how information is transformed according to a given rule. The exam presents words, letters, or numbers encoded in a systematic way, and you must decode new words using the same logic or determine the code for a given word.

Key ideas

• Letter-to-letter coding: Each letter in a word is replaced by another letter following a fixed rule—commonly forward/backward shifts in the alphabet (e.g., A→C means +2 shift), reverse alphabet substitution (A↔Z, B↔Y), or a combination of both.
• Letter-to-number coding: Letters are converted to their positional values (A=1, B=2, … Z=26) or codes derived from those values (sum, product, difference). Understanding the 1–26 position system is foundational.
• Reverse alphabet pairing: A critical shortcut—memorise that A↔Z (1+26=27), B↔Y (2+25=27), and so on. If a letter at position n has reverse position (27 − n), pattern detection becomes instant.
• Conditional coding: The encoding rule changes based on the letter's characteristics—vowel vs. consonant, position in the word (first, middle, last), or whether the letter repeats. These questions require careful observation of which letters get special treatment.
• Word-level operations: Some codes are not letter-by-letter but apply arithmetic to the entire word—total positional sum, number of vowels × number of consonants, or coding based on word length.

Watch out for

• Ignoring wraparound in shifts: When adding +3 to Y (position 25), students write position 28 instead of wrapping to B (position 2). Correct method: 25+3=28, then 28−26=2 (B). Always subtract 26 if result exceeds 26, add 26 if below 1.
• Confusing reverse alphabet with backward shift: Reverse alphabet means A↔Z (opposite ends pairing), not A → Z direction. A −1 shift makes A become Z due to wraparound, but that's different from reverse substitution.
• Mixing up position and shift value: Students often add the letter's position to itself instead of the shift constant. If the rule is +2, and you're coding C (position 3), the answer is position 3+2=5 (E), not 3+3=6.

Quick reference

• Alphabet positions: A=1, E=5, J=10, M=13, P=16, T=20, Z=26.
• Reverse formula: Position of reverse letter = 27 − original position.
• Shift rule check: Test first and last letters of the example word to quickly spot uniform shifts.
• Vowel set: A, E, I, O, U—memorise to handle conditional vowel coding instantly.
• Two-way verification: After finding a pattern, encode one example and see if you get the given code; if yes, your rule is likely correct.

Check yourself: 3 questions

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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