Classification

Classification — Odd One Out

Overview

Classification is one of the most frequently tested reasoning topics in the Maharashtra Police Bharti exam. The concept is simple: you are given a group of items (words, numbers, letters, or figures), and you must identify the one that does not belong with the others. This tests your ability to quickly recognise common properties and spot the exception.

This topic appears in almost every reasoning section because it requires no complex calculations—just sharp observation and pattern recognition. Mastering classification gives you easy marks and builds the analytical thinking needed for other reasoning topics like analogies and series.

Students must learn to identify multiple possible grouping criteria (meaning, category, position, mathematical property, visual feature) and then determine which criterion applies to the majority. The odd item is simply the one that breaks the pattern.

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Key Concepts

• Classification principle: Four or five items share a common property; exactly one item lacks that property and is the "odd one out."
• Verbal classification: Words grouped by meaning (fruits, metals, rivers), grammatical category (verbs vs nouns), origin, or thematic relation.
• Numerical classification: Numbers grouped by mathematical property—prime, even, odd, perfect square, divisible by a certain number, or following a pattern.
• Letter/Alphabet classification: Letters grouped by position (vowels, consonants), position in alphabet (odd/even positions), or pattern in letter codes.
• Figural classification: Shapes grouped by number of sides, open/closed figures, shading, rotation direction, or presence of specific elements.
• Multiple properties: Sometimes items share more than one property; identify the most specific or most obvious common link.
• Elimination approach: When stuck, check each option against the others and count how many share a particular feature.

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Formulas / Key Facts

1. Vowels in English: A, E, I, O, U (positions 1, 5, 9, 15, 21 in alphabet)
2. Prime numbers up to 50: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47
3. Perfect squares up to 200: 1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144, 169, 196
4. Perfect cubes up to 250: 1, 8, 27, 64, 125, 216
5. Alphabet positions: A=1, B=2, ... Z=26. Quick check: J=10, T=20.
6. Sum of opposite alphabet pairs: A+Z = 1+26 = 27, B+Y = 2+25 = 27, and so on.
7. Common categories in verbal questions: Planets, states, capitals, rivers, metals, diseases, vitamins, sports, musical instruments.
8. Figural cues: Count sides, check symmetry, note shading (filled/empty), observe rotation (clockwise/anticlockwise).

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Worked Examples

Example 1 — Verbal Classification

Question: Find the odd one out: (A) Apple (B) Mango (C) Potato (D) Banana

Solution:

• Apple, Mango, Banana → Fruits
• Potato → Vegetable (root/tuber)
• Common property: Fruits
• Answer: (C) Potato

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Example 2 — Numerical Classification

Question: Find the odd one out: (A) 27 (B) 37 (C) 47 (D) 57

Solution:

• Check if numbers are prime:
  • 27 = 3 × 9 → Not prime
  • 37 → Prime
  • 47 → Prime
  • 57 = 3 × 19 → Not prime
• Wait, two are not prime. Try another approach.
• Check pattern: 27, 37, 47, 57 — difference is 10 each.
• But 27 = 3³ (perfect cube), others are not cubes.
• Actually, simpler: 37, 47 are prime; 27, 57 are not.
• Re-check: Among options, 37 and 47 are prime. 27 and 57 are composite.
• Most likely intended answer: 27 stands out as a perfect cube.
• Answer: (A) 27 (perfect cube; others are not)

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Example 3 — Letter Classification

Question: Find the odd one out: (A) BD (B) FH (C) JL (D) MO

Solution:

• Check positions: B=2, D=4 (gap of 2, both even)
• F=6, H=8 (gap of 2, both even)
• J=10, L=12 (gap of 2, both even)
• M=13, O=15 (gap of 2, but both ODD positions)
• Pattern: First three pairs have even-positioned letters.
• Answer: (D) MO (odd-positioned letters, unlike others)

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Example 4 — Figural Classification

Question: Four figures show: Triangle, Square, Pentagon, Circle. Find the odd one.

Solution:

• Triangle → 3 sides
• Square → 4 sides
• Pentagon → 5 sides
• Circle → 0 sides (curved, no straight edges)
• Common property: Polygon with straight sides
• Answer: Circle (not a polygon)

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Common Mistakes

1. Choosing the first difference you see → Always verify that three or four items share one property and only one item differs. Check all options before finalising.
2. Ignoring mathematical properties for numbers → Students often look only at odd/even. Also check: prime, composite, perfect square, perfect cube, divisibility by 3/7/11.
3. Confusing alphabet position with letter itself → "E is odd" is wrong thinking. E is at position 5, which is odd. The letter E itself is a vowel. Know what property the question tests.
4. Overlooking subtle figural differences → In figure questions, students miss small details like one figure being open (incomplete boundary) while others are closed. Always scan for: shading, rotation, number of elements, symmetry.
5. Assuming only one valid answer exists without checking → Occasionally, exams have ambiguous questions. If two properties seem valid, choose the more commonly tested one (e.g., "prime vs composite" is more standard than "sum of digits").

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Quick Reference

• Odd one out = the item that breaks the common pattern.
• Verbal: Think category (fruit/vegetable, country/city, mammal/reptile).
• Numbers: Check prime, square, cube, even/odd, divisibility.
• Letters: Check vowel/consonant, position (odd/even), gap between letters.
• Figures: Count sides, check open/closed, note shading and rotation.
• Time tip: Spend maximum 45 seconds; if stuck, mark and move on.