Classification (Odd One Out) — SSC CGL Reasoning

Classification flips analogy on its head: instead of "A is to B as C is to ?", you're given four (or five) items and must find the one that breaks the rule the rest follow. The whole game is finding that rule quickly — and, crucially, finding the most specific rule, because a loose rule often lets two answers through. Words test category, numbers test arithmetic properties, letters test position patterns.

1. What SSC actually asks

Tier 1: 2–3 Q · Tier 2: 2–3 Q. Formats: word classification (which word is a different kind of thing), number classification (which number lacks a shared property), letter/letter-cluster classification (which group breaks a positional pattern), and mixed GK classification (countries vs a city, metals vs an alloy).

2. Word classification — find the category

Ask "what are the other three, specifically?"

• Rose, Lotus, Marigold, Mango → three flowers, one fruit.
• Copper, Iron, Gold, Brass → three pure metals, one alloy.
• Look for the tightest category: if three are root vegetables and one a leafy vegetable, "vegetable" is too loose — the intended rule is narrower.

3. Number classification — the property checklist

Run a fast mental checklist on the set:

1. Prime / composite — e.g. 3, 5, 11, 17 prime; 14 breaks it.
2. Perfect square / cube — 8, 27, 64, 125 are cubes; 100 breaks it.
3. Divisibility — 10, 25, 45, 60 divisible by 5; 54 breaks it.
4. Even/odd, digit sum, digit relationship — 4, 16, 36, 64 are even squares; 49 (odd square) breaks it.

Test the cheapest properties first (parity, divisibility by 5), then squares/cubes, then primes.

4. Letter classification — position and gaps

Convert letters to positions (A = 1 … Z = 26) and look at the gap pattern:

• AD, EH, IL, MP all have a gap of 3; QU (gap 4) breaks it.
• BCD, FGH, LMN, PQR are three consecutive consonants; STU contains the vowel U.
• Also check: all-vowels vs one consonant, mirror letters (A↔Z, B↔Y), or a fixed skip (+2, +4) between clusters.

5. The "two answers" trap

If two options both seem odd, your rule is too loose — a stricter rule is intended.

• 4, 9, 16, 25, 36 — all perfect squares, but 4, 16, 36 are even squares and 9, 25 odd. If only one odd answer is allowed, the intended property is narrower (e.g. "square of a prime": 4, 9, 25 vs 16, 36).
• When stuck, find the property exactly three items share; the fourth is your answer.

6. Solved PYQ-style examples

Q1. Odd one out: Rose, Lotus, Marigold, Mango. Solution. Rose, Lotus, Marigold are flowers; Mango is a fruit.

Q2. Odd one out: 3, 5, 11, 14, 17. Solution. All are prime except 14 (also the only even number).

Q3. Odd one out: 8, 27, 64, 100, 125. Solution. $2^3,3^3,4^3,5^3$ are perfect cubes; 100 is not a cube.

Q4. Odd one out: AD, EH, IL, MP, QU. Solution. Gaps: AD, EH, IL, MP each span 3 letters; QU spans 4 (Q17 → U21).

Q5. Odd one out: BCD, FGH, LMN, PQR, STU. Solution. The first four are three consecutive consonants; STU includes the vowel U.

Q6. Odd one out: 10, 25, 45, 54, 60. Solution. All are divisible by 5 except 54.

7. Exam protocol

1. For words, name the specific category the majority share, then find the outsider.
2. For numbers, run the checklist: parity → divisibility → squares/cubes → primes.
3. For letters, convert to positions and compare gaps, vowels and mirror pairs.
4. Two candidates? Your rule is too loose — tighten it until exactly one item breaks.
5. Don't overthink easy ones; the intended rule is usually the first specific pattern you spot.