Classification (Odd One Out)
About 6 min · Reasoning Ability · English
Time worked out from the lesson's 372 words at 150 words a minute, plus a minute for each question.
Classification, commonly called "Odd One Out," is a fundamental reasoning topic that tests your ability to identify patterns and categorize items based on shared characteristics.
Key ideas
- Common Property Principle: In every classification question, all items except one share a common property. Your job is to find that property and identify the outsider.
- Multiple Valid Properties: A group may have several possible classification bases. Always choose the most specific or dominant property that excludes exactly one item.
- Word-Based Classifications: Items grouped by category (fruits, metals, rivers), grammatical features (parts of speech, gender), origin (languages, countries), or functional use (tools, instruments).
- Number-Based Classifications: Items grouped by mathematical properties—prime numbers, perfect squares, even/odd, divisibility rules, or number patterns (sum of digits, difference between digits).
- Letter-Based Classifications: Items grouped by position in alphabet (vowels, consonants), pattern in positions (consecutive letters, gap patterns), or symmetry (letters with vertical/horizontal symmetry).
Watch out for
- Stopping at the first property noticed → Always verify your answer works. If you think "all are two-digit numbers," check if ALL items including your chosen answer fit that pattern. The odd one out must violate the rule that others follow.
- Ignoring mathematical properties in number questions → Students often look for digit patterns (sum of digits, number of digits) when the actual basis is prime/composite, perfect square/cube, or divisibility. Check mathematical properties first for number-based questions.
- Confusing similar categories → "Planet" vs "Star," "Metal" vs "Non-metal," "Mammal" vs "Reptile"—these require precise knowledge. If Whale appears with Fish names, remember Whale is a mammal.
Quick reference
- Convert letters to positions immediately: A=1, B=2 ... Z=26
- For numbers: check prime, perfect square, perfect cube first
- For words: identify category (fruit/flower/city/river/country)
- One item must be different—if you can't find it, try a different property
- Gap patterns in letters: subtract positions to find the rule
Check yourself: 3 questions
1. Find the odd one out from the following group: A) 7 B) 13 C) 21 D) 19
2. Find the odd one out from the following group: A) Mango B) Apple C) Potato D) Orange
3. Find the odd one out from the following group: A) 3, 9, 27 B) 2, 8, 32 C) 4, 16, 64 D) 5, 25, 125
This lesson is cut from the topic's note, not rewritten. Fact-checked on 18 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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