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SSC CGL Classification / Odd One Out

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This page covers SSC CGL Classification / Odd One Out with complete concept notes, 51 graded practice MCQs, key points and exam-specific tips. Free to study.

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Concept Notes

Classification / Odd One Out— Rules & Concept

Core ConceptRead this first — the foundation of the topic
Think of it like this

If someone gives you Apple, Mango, Carrot, Banana — Carrot is the odd one out because the other three are fruits and carrot is a vegetable

SSC CGL asks this in 3 formats

• Word-based (names, objects, places) • Number-based (series of numbers) • Letter/Alphabet-based (letter groups) ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ KEY RULES / PROPERTIES ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Rule 1 — Always find the MAJORITY GROUP first. Three items form the group. One breaks it. Never pick the answer before checking all four options. Rule 2 — One common property connects three items

That property can be

category, shape, colour, mathematical property, position in alphabet, historical period, geography, etc. Rule 3 — In number-based questions, check: odd/even, prime/composite, perfect square, perfect cube, sum of digits, number of factors. Rule 4 — In letter-based questions, check: vowels/consonants, position values (A=1, B=2... Z=26), number of letters, alphabetical gaps between letters. ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Formula BlockMemorise — at least one formula appears in every paper

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For number-based odd one out:

• Perfect Square check: n x n (1,4,9,16,25,36,49,64,81,100...)

• Perfect Cube check: n x n x n (1,8,27,64,125,216...)

• Prime Number: divisible only by 1 and itself

• Sum of digits trick: add all digits of each number, see which total breaks the pattern

• Number of factors trick: if 3 numbers have even number of factors but one has odd number of factors (perfect squares have odd number of factors) — that one is different

For letter-based odd one out:

• Position value formula: A=1, B=2, C=3 ... Z=26

• Gap formula: Subtract position values of letters in a group to find the pattern gap

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Exam PatternsWhat examiners ask — read before attempting PYQs
Pattern 2 — Number property

4 numbers where 3 are prime, one is not. Or 3 are perfect squares, one is not

Pattern 3 — Letter group

Groups like ACE, BDF, GIK, HJL — find the one that breaks the +2 gap pattern

Pattern 4 — Analogy-based classification

All three follow same relationship pattern except one. ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

ShortcutsUse these to save 30–60 seconds per question
TRICK 2 — SUM OF DIGITS SHORTCUT

For large numbers, quickly add digits

Example

121 → 1+2+1=4, 144 → 1+4+4=9, 169 → 1+6+9=16, 196 → 1+9+6=16. See which digit sum breaks pattern

TRICK 3 — ALPHABET POSITION SHORTCUT

Memorise that M=13 is the middle letter. Letters before M are 1-13, after M are 14-26. This helps quickly calculate positions without writing the full alphabet. ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Worked ExampleSolve this step-by-step before moving on

— WORD BASED ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Question: Find the odd one out — Cobra, Python, Chameleon, Krait Step 1 — Identify each item: • Cobra — Venomous snake • Python — Non-venomous snake • Chameleon — Lizard (reptile but NOT a snake) • Krait — Venomous snake Step 2 — Find the majority group: Cobra, Python, Krait — all three are SNAKES. Step 3 — Find the odd one: Chameleon is a lizard, not a snake. Answer: Chameleon NOTE: Do not fall for the trap of grouping by 'venomous vs non-venomous'. Python is non-venomous but still a snake — so it stays in the group. The broader category wins. ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ WORKED EXAMPLE 2 — NUMBER BASED ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Question: Find the odd one out — 17, 23, 31, 33 Step 1 — Check if each number is prime: • 17 — divisible by 1 and 17 only → PRIME • 23 — divisible by 1 and 23 only → PRIME • 31 — divisible by 1 and 31 only → PRIME • 33 — divisible by 3 and 11 also (3x11=33) → NOT PRIME — COMPOSITE Step 2 — Majority group: 17, 23, 31 are all prime numbers. Step 3 — Odd one out: 33 is composite. Answer: 33 Quick check shortcut: 33 ends in 3, looks prime — but 3+3=6, divisible by 3.

So 33 is divisible by 3. Always check divisibility rules quickly. ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Exam TrapsCommon mistakes students make — avoid these

— THE NUMBER 1 TRAP ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ THE TRAP: Students pick an answer based on the FIRST difference they spot instead of finding the MAJORITY GROUP first. Example: In the question — Parrot, Crow, Bat, Eagle — many students pick Bat (only mammal, cannot fly by flapping wings like birds). But some students pick Parrot because it can talk, or Crow because it is black. These are WRONG logic paths. Correct method: Always ask — which THREE share the strongest, most obvious common feature?

Then the fourth is automatically the answer. Remember: The examiner intentionally puts one item that LOOKS like the odd one out but is NOT. Always verify your answer by confirming the group of three.

Key Points to Remember

  • Odd One Out = find 3 items with a common property; the 4th that breaks the pattern is the answer.
  • Always use the 3-1 Rule: identify the group of THREE first, then the odd one falls out automatically.
  • For number questions, check: prime/composite, odd/even, perfect square, perfect cube, sum of digits.
  • Perfect squares have an ODD number of factors — use this to spot them instantly (1, 4, 9, 16, 25, 36...).
  • Alphabet position formula: A=1, B=2, C=3... Z=26. M=13 is the midpoint — memorise this.
  • Gap formula for letter groups: subtract position values to find the pattern gap (e.g., +2, +3, +4).
  • Sum of digits shortcut: add all digits of a large number quickly to find divisibility and pattern breaks.
  • In word-based questions, always choose the BROADEST category to define the group (e.g., snake beats venomous).
  • The number 1 is NEITHER prime NOR composite — it is a unique number; treat it as special in classification.
  • Trap alert: Do NOT pick the answer on first instinct — always verify by confirming the other THREE form a valid group.

Exam-Specific Tips

  • The number 1 is neither prime nor composite — it is the only such positive integer and is a frequent odd one out trap in SSC exams.
  • Perfect squares always have an odd number of factors because one factor (the square root) pairs with itself — e.g., 36 has factors 1,2,3,4,6,9,12,18,36 = 9 factors (odd).
  • 2 is the ONLY even prime number — all other prime numbers are odd; this makes 2 a frequent odd one out in prime number sets.
  • Alphabet position values: A=1, B=2, C=3, M=13, N=14, Z=26 — M is the 13th letter and exact midpoint of the alphabet.
  • In SSC CGL Tier-1, Classification / Odd One Out typically contributes 3-5 questions out of 25 in the Reasoning section.
  • Divisibility rule for 3: if sum of digits is divisible by 3, the number is divisible by 3 — e.g., 33: 3+3=6, divisible by 3, so 33 is NOT prime.
  • A perfect cube series: 1, 8, 27, 64, 125, 216, 343, 512, 729, 1000 — memorise at least up to 10 cubed for quick identification.
  • Composite numbers start from 4 — the smallest composite number is 4 (2x2); 1 is not composite, 2 and 3 are prime.
Practice MCQs

Classification / Odd One Out — Practice Questions

51graded MCQs · easy to hard · full solution & trap analysis · showing 20 of 51

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Practice 1easy

Find the odd one out: Piano, Guitar, Flute, Violin

Practice 2easy

Find the odd one out: Orange, Banana, Carrot, Apple

Practice 3easy

Find the odd one out: Rose, Lotus, Lily, Cactus

Practice 4easy

Which one of the following does NOT belong to the group? A) Cricket B) Tennis C) Badminton D) Chess

Practice 5easy

Which one of the following is the odd one out? A) Carrot B) Potato C) Brinjal D) Tomato

Practice 6easy

Which one of the following is the odd one out? Pencil, Pen, Eraser, Sharpener

Practice 7easy

Which one of the following does NOT belong to the group? A) Carrot B) Potato C) Tomato D) Onion

Practice 8easy

Find the odd one out: Sparrow, Penguin, Eagle, Parrot

Practice 9easy

Which one of the following does NOT belong to the group? A) Gold B) Silver C) Copper D) Oxygen

Practice 10easy

Which one of the following is the odd one out? Sparrow, Penguin, Eagle, Parrot

Practice 11easy

Find the odd one out: Mango, Carrot, Broccoli, Spinach

Practice 12easy

Which one of the following does NOT belong to the group? A) Sparrow B) Penguin C) Ostrich D) Kiwi

Practice 13easy

Four words are given below. Three of them share a common property. Find the odd one out. Rose, Lotus, Tulip, Marigold

Practice 14easy

Which one of the following is the odd one out? Doctor, Teacher, Engineer, Patient

Practice 15easy

Find the odd one out: Sparrow, Eagle, Penguin, Parrot

Practice 16easy

Find the odd one out: Rose, Tulip, Sunflower, Carrot

Practice 17easy

Which one of the following is the odd one out? Apple, Carrot, Potato, Spinach

Practice 18medium

Which one of the following does NOT belong to the same category? A) Mercury B) Venus C) Earth D) Moon

Practice 19medium

In a classification task, which one of the following does NOT belong to the same group as the others? A) Carrot B) Potato C) Tomato D) Onion

Practice 20medium

Which one of the following does NOT belong to the same group? A) Violin B) Guitar C) Flute D) Sitar

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60-Second Revision — Classification / Odd One Out

  • Remember: Always find the GROUP OF THREE first — the one left out is your answer. Never guess from one item alone.
  • Formula: For number classification — check prime/composite, perfect square (n²), perfect cube (n³), sum of digits, and number of factors.
  • Formula: Alphabet position A=1 to Z=26, M=13 is midpoint. Subtract position values to find the letter gap pattern.
  • Trap: The number 1 is NEITHER prime NOR composite — treat it as a standalone special case in number classification.
  • Trap: Do NOT classify by a minor or superficial feature — always use the BROADEST and most OBVIOUS common property shared by three items.
  • Shortcut: For large numbers, use sum of digits to check divisibility by 3 or 9 instantly — saves time in exams.
  • Remember: 2 is the only even prime number. If you see 2 with odd primes, do not eliminate 2 unless the pattern clearly demands it.
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