Classification (Odd One Out)

Subject: Mental Ability | Frequency: 2-3 questions per APPSC paper | Time: 30-45 sec/question

Introduction

Classification questions present 4-5 items where all but one share a common property. You must find the odd one out. APPSC favours category-based (fruits, planets) and number-based (prime, square) classifications. The key skill is checking multiple classification bases before answering.

Core Method

1. Read all options carefully — understand each item
2. Identify the common property — what do 3 or 4 items share?
3. Find the exception — which item does NOT share this property?
4. Verify — confirm ALL other items fit and ONLY the odd one doesn't
5. Check alternative bases — if multiple classifications exist, pick the most logical one

Types with Examples

Worked Examples — Easy

Q1: Apple, Mango, Potato, Banana

• Apple, Mango, Banana = fruits; Potato = vegetable
• Answer: Potato

Q2: 2, 5, 11, 14, 17

• 2, 5, 11, 17 are prime; 14 = 2 x 7 (not prime)
• Answer: 14

Q3: Cricket, Football, Chess, Hockey

• Cricket, Football, Hockey = outdoor/physical sports; Chess = indoor board game
• Answer: Chess

Worked Examples — Medium

Q4: 1, 4, 9, 15, 25, 36

• 1=1², 4=2², 9=3², 25=5², 36=6²; 15 is NOT a perfect square
• Answer: 15

Q5: AZ, BY, CX, DW, EU

• A(1)+Z(26)=27, B(2)+Y(25)=27, C(3)+X(24)=27, D(4)+W(23)=27
• E(5)+U(21)=26 — does NOT sum to 27
• Answer: EU (should be EV)

Q6: Mercury, Venus, Moon, Jupiter, Saturn

• Mercury, Venus, Jupiter, Saturn = planets; Moon = satellite
• Answer: Moon

Worked Examples — Hard

Q7: 121, 169, 196, 225

• 121=11², 169=13², 196=14², 225=15²
• Pattern: squares of 11, 13, 15 are odd numbers; 14 breaks the odd-number sequence
• Answer: 196 (14² breaks the odd-number square pattern)

Q8: 8, 27, 64, 100, 125

• 8=2³, 27=3³, 64=4³, 125=5³; but 100=10² (not a cube)
• Answer: 100

Q9: BDFI, CEGJ, DFHK, EGIL

• Expected pattern: +2, +2, +2 within each group
• CEGJ: C(3),E(5),G(7),J(10) — gaps 2,2,3 (last gap breaks)
• BDFI: B(2),D(4),F(6),I(9) — gaps 2,2,3 (also breaks)
• But BDFI is the one that should be BDFH — last letter breaks the +2 pattern
• Answer: BDFI

Shortcuts & Tricks

Common Mistakes

1. Jumping to the first pattern noticed — always check if a BETTER classification exists
2. Ignoring mathematical properties — not checking prime, square, cube for number groups
3. GK gaps — not knowing which item belongs to which category
4. Alphabet position errors — miscounting letter positions, especially after J=10
5. Not verifying all items — confirming only 2-3 items fit instead of all remaining ones

Exam Strategy

• First check category, then mathematical property, then linguistic pattern — this order covers 90%+ of questions
• APPSC keeps difficulty at easy-to-medium
• Time: 30-45 seconds per question
• If two bases seem equally valid, the more fundamental one (category > math > linguistic) is usually the intended answer
• Negative marking: -0.333 — skip if genuinely confused between two items

Practice Questions

1. Rose, Lily, Dog, Jasmine → Dog (others are flowers)
2. 2, 3, 5, 9, 11 → 9 (others are prime)
3. January, March, June, July → June (others have 31 days)
4. 4, 9, 16, 25, 32 → 32 (others are perfect squares)
5. Pen, Pencil, Eraser, Hammer → Hammer (others are stationery)

Key Terms / Formulas