Classification (Odd One Out)
Classification (Odd One Out) is a frequently tested area in CUET General Test. Work through these free NTA-style sample questions with full answers and explanations, then attempt all 30 in a timed practice test to build exam-day speed.
Snapshot
- Classification (Odd One Out) gives you four or five items. Four share a hidden property; one breaks it. Your job is to find that one.
- The skill is to name what the majority have in common first. Never start by staring at a "strange-looking" item, because that is how you pick the wrong answer.
- CUET dresses this up as words (a common category), numbers (prime, square, cube, divisibility), letters and letter groups (position patterns) and pairs (a hidden relationship inside each pair).
- A correct rule isolates exactly one item. If your rule leaves two items out, it is the wrong rule. Exam reality: +5 for a correct answer and −1 for a wrong one.
Part 1 — The method: rule first, exception second
Written and reviewed by Devendra Dubey, Mathematics & Commerce faculty at UniDrill (M.Sc. Mathematics, Osmania University · 10 years teaching). Prepared for the CUET UG General Test.
Odd-one-out questions look like a hunt for the strange item. They are really a hunt for the rule. Once you name the rule that four items obey, the fifth item is obvious, and you can check your answer by confirming that the rule fails for it alone.
| Step | What to do | Why it matters |
|---|---|---|
| 1. Identify the item type | Words, numbers, letters, letter groups, or pairs | Tells you which checklist to run |
| 2. Find the majority property | Look for a property that at least three items share | Prevents fixating on one item |
| 3. Name the rule in a short phrase | "These are all prime", "These are all birds" | A named rule is testable |
| 4. Test the rule on every item | Count exactly how many obey it | You need four obeying, one failing |
| 5. If two fail, change the rule | Try the next property on the checklist | Two odd ones means the wrong property |
| 6. Read the question again | The answer is the exception, not the rule | A common slip when you are rushing |
The two-odd-ones test. Suppose the set is 2, 3, 5, 7, 9. With the rule "prime", only 9 fails. With the rule "odd", only 2 fails. Both rules isolate exactly one item, which means the set is genuinely ambiguous. Real questions are written so that only one of these rules works across all five items and the options will not let both answers appear. Whenever you find yourself with two possible answers, look for a sharper rule (a rule that captures all four of the others at once).
Pause and predict: In the set 3, 5, 7, 11, 12, which rule isolates one item, and which item is it?
Check your answer: The first four are prime numbers and also odd numbers; 12 is composite and even. Both the rule "prime" and the rule "odd" isolate 12, so there is no ambiguity.
Part 2 — The full menu of classification questions
| Type | What you see | The rule you look for |
|---|---|---|
| Words, plain category | Rose, Lotus, Lily, Mango, Jasmine | A shared category (flowers) |
| Words, function | Pen, Pencil, Chalk, Eraser, Marker | A shared use (writing tools) |
| Words, hidden property | Whale, Dolphin, Shark, Seal, Porpoise | A shared biology (mammals) |
| Numbers, single | 17, 23, 29, 33, 41 | Prime, square, cube, multiple |
| Number pairs | (4, 16), (5, 25), (6, 36), (8, 60) | A rule joining the two numbers in each pair |
| Number triples | (3, 4, 5), (5, 12, 13), (6, 8, 10), (7, 24, 25) | Triples with a shared property |
| Letters, single | A, E, I, O, T | Vowels versus consonants |
| Letter groups | ACE, FHJ, KMO, PRT, UWZ | Constant gap between letters |
| Alpha-numeric | B2, D4, F6, H8, J11 | Letter position equals the number |
| Odd pair of words | Doctor : Hospital, Teacher : School, Surgeon : Scalpel | Which pair has a different relationship |
| Odd one by spelling | Words with the same count of letters or vowels | A structural property of the word |
Part 3 — Numbers: the checklist
Run the checklist in this order. The earlier properties are the commonest, so you save time by trying them first.
| Check | How to test | Example set and its odd one |
|---|---|---|
| Prime | No divisors other than 1 and itself | 17, 23, 29, 33, 41 (33 = 3 × 11) |
| Perfect square | Square root is a whole number | 121, 144, 169, 196, 220 (220 is not a square) |
| Perfect cube | Cube root is a whole number | 27, 64, 125, 216, 250 (250 is not a cube) |
| Same parity | All even or all odd | 14, 22, 38, 46, 51 (51 is odd) |
| Common multiple | Divisible by the same number | 18, 27, 36, 45, 52 (multiples of 9) |
| Digit sum | The digits add to the same total | 18, 27, 36, 45, 52 (digit sums 9, 9, 9, 9, 7) |
| n² ± 1 or n³ ± 1 | Each is one more or one less than a square or cube | 3, 8, 15, 24, 34 (n² − 1 gives 35, not 34) |
| Palindromes | The number reads the same backwards | 121, 232, 343, 454, 465 |
| Digit pattern | Digits in order, repeating, or reversed | 123, 234, 345, 456, 468 |
| Fibonacci-like | Each is the sum of the two before it | 2, 3, 5, 8, 12 (13 would fit) |
Know these lists cold. They are the raw material of this section.
| List | Values |
|---|---|
| Primes up to 50 | 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47 |
| Squares 1 to 20 | 1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144, 169, 196, 225, 256, 289, 324, 361, 400 |
| Cubes 1 to 10 | 1, 8, 27, 64, 125, 216, 343, 512, 729, 1000 |
Divisibility quick tests. A number is divisible by 3 if its digit sum is; by 9 if its digit sum is a multiple of 9; by 4 if its last two digits are; by 6 if it is even and divisible by 3; by 11 if the difference between the sum of digits in odd places and in even places is 0 or a multiple of 11.
A note on 1 and 2. The number 1 is neither prime nor composite. The number 2 is the only even prime. Questions that include them are usually testing exactly this.
Part 4 — Letters and letter groups
Convert letters to positions (A = 1 ... Z = 26). Then look for one of these.
| Pattern | Example | Odd one |
|---|---|---|
| Constant gap inside every group | ACE, FHJ, KMO, PRT, UWZ | UWZ (gap 2 then 3; others have gap 2) |
| Constant gap between the start letters | AC, EG, IK, MO, QT | QT (inner gap 3 while the others have 2) |
| Vowel versus consonant | E, I, O, K, U | K |
| Letters whose positions are odd or even | B, D, H, K, P | K (position 11 is odd; the rest are even) |
| Mirror pairs | AZ, BY, CX, DW, EU | EU (mirror of E is V, not U) |
| Vertical symmetry | Letters that look the same in a mirror: A, H, I, M, N | N, which is not symmetric about a vertical line |
Alpha-numeric items. Check whether the number is the letter position (B2, D4), twice the position, or a fixed offset. B2, D4, F6, H8, J11 follows "number equals position" and J would need 10, so J11 is odd.
Part 5 — Words: names of categories
When you read the words, name a category the moment three of them agree. Keep these families in mind.
| Family | Typical members | Common odd-one-out twist |
|---|---|---|
| Birds | Sparrow, Eagle, Parrot, Crow | Bat is a mammal; Butterfly is an insect |
| Mammals | Whale, Dolphin, Cow, Bat | Shark is a fish |
| Metals | Iron, Copper, Gold, Zinc | Diamond (carbon) and Sulphur are non-metals |
| Planets | Mercury, Venus, Mars, Jupiter | Moon is a satellite; Sun is a star |
| Rivers | Ganga, Yamuna, Godavari, Krishna | Himalaya is a mountain range |
| Two-dimensional shapes | Triangle, Square, Circle, Pentagon | Cube and Sphere are three-dimensional |
| Fruits, vegetables, cereals | Mango, Apple, Banana; Wheat, Rice, Maize | Potato is a vegetable among fruits; Cotton is a fibre crop among cereals |
| Writing tools | Pen, Pencil, Chalk, Marker | Eraser removes marks, it does not write |
| Months with 31 days | January, March, May, July | June has 30 days |
Overlapping categories. Some items belong to two families. A tomato is a vegetable in the kitchen and a fruit in botany. A whale lives in water but is a mammal. When an item fits two groups, let the other four items decide. In Tomato, Potato, Brinjal, Onion, Apple the four vegetables rule, so Apple is odd. In Mango, Apple, Banana, Orange, Tomato the four fruits rule, so Tomato is odd. The question writer intends a rule that leaves exactly one exception.
Function over appearance. For tools and objects, classify by what they do. Pen, Pencil, Chalk and Marker write; the eraser removes writing.
Part 6 — Worked examples with full reasoning
1. 17, 23, 29, 33, 41. Check "prime": 17, 23, 29 and 41 are prime. 33 = 3 × 11 is composite. The odd one is 33. (Also check parity: all five are odd, so parity cannot be the rule.)
2. 27, 64, 125, 216, 250. Check "cube": 3³ = 27, 4³ = 64, 5³ = 125, 6³ = 216. 250 is not a cube (6.3³ is about 250). The odd one is 250.
3. 121, 144, 169, 196, 220. These are 11², 12², 13², 14². The next square is 225, so 220 breaks it.
4. 18, 27, 36, 45, 52. Divisibility by 9: 18, 27, 36 and 45 are multiples of 9 and have digit sum 9. 52 has digit sum 7. The odd one is 52.
5. 15, 25, 35, 45, 54. Four numbers end in 5. 54 does not. The odd one is 54.
6. Mercury, Venus, Mars, Moon, Jupiter. Mercury, Venus, Mars and Jupiter are planets. The Moon is a natural satellite of the Earth. The odd one is Moon.
7. Sparrow, Eagle, Bat, Parrot, Crow. Sparrow, Eagle, Parrot and Crow are birds. A bat flies but is a mammal. The odd one is Bat. (Flying is not the rule, because then Bat would belong and nothing would be left out.)
8. Ganga, Yamuna, Godavari, Himalaya, Krishna. Four are rivers. Himalaya is a mountain range. The odd one is Himalaya.
9. Triangle, Square, Rectangle, Cube, Pentagon. Four are flat two-dimensional shapes. The cube is a three-dimensional solid. The odd one is Cube.
10. AC, EG, IK, MO, QT. Convert to positions: AC = 1, 3; EG = 5, 7; IK = 9, 11; MO = 13, 15; QT = 17, 20. The inner gap is 2 in the first four, but 3 in QT. The starting letters also step by 4 (1, 5, 9, 13, 17), so only the inner gap fails. The odd one is QT.
11. ACE, FHJ, KMO, PRT, UWZ. Positions: 1-3-5, 6-8-10, 11-13-15, 16-18-20, 21-23-26. The first four have gaps 2 and 2 and start at 1, 6, 11, 16 (a step of 5). The last group has gaps 2 and 3 (UWY would have fitted). The odd one is UWZ.
12. (4, 16), (5, 25), (6, 36), (7, 49), (8, 60). In each pair the second number is the square of the first, except 8 whose square is 64. The odd one is (8, 60).
13. 121, 232, 343, 454, 465. The first four are palindromes. 465 reads 564 backwards. The odd one is 465.
14. Doctor : Hospital, Teacher : School, Surgeon : Scalpel, Judge : Court, Chef : Kitchen. Four pairs are professional : place of work. Surgeon : Scalpel is worker : tool. The odd pair is Surgeon : Scalpel.
Part 7 — Common traps
| Trap | Why it is tempting | The truth |
|---|---|---|
| Fixating on one strange-looking item | It stands out immediately | Find what four items share first |
| Rule leaves two odd ones | You stop at the first rule that seems fine | Two odd ones means the rule is wrong; look for a sharper rule |
| Overlapping categories | Tomato, whale, peanut | Choose the intended family from the other four items |
| Judging letter gaps by eye | The alphabet looks even | Convert to positions and count |
| Ignoring parity | Prime numbers feel enough | Test odd and even before you commit to prime |
| 1 and 2 in a prime set | They look "like primes" | 1 is not prime; 2 is the only even prime |
| Picking the rule instead of the exception | You solve it and then mark the wrong thing | The answer is the item that breaks the rule |
| Surface similarity in words | Two words share a first letter | Group by meaning and function, not spelling, unless the question is about spelling |
| Treating pairs as single numbers | The pair looks like two items | In pair questions, the rule connects the two numbers in each pair |
Part 8 — Rapid-fire practice
Name the rule before you name the odd one. Check your answers against the table.
| No. | Set | Odd one | Rule |
|---|---|---|---|
| 1 | 2, 3, 5, 7, 9 | 9 | Primes |
| 2 | 16, 36, 49, 64, 80 | 80 | Perfect squares |
| 3 | 8, 27, 64, 100, 125 | 100 | Perfect cubes |
| 4 | Iron, Copper, Gold, Diamond, Zinc | Diamond | Metals |
| 5 | Cow, Buffalo, Goat, Hen, Horse | Hen | Mammals; hen is a bird |
| 6 | Mango, Apple, Potato, Banana, Grapes | Potato | Fruits |
| 7 | 11, 13, 17, 19, 21 | 21 | Primes (21 = 3 × 7) |
| 8 | 14, 28, 42, 56, 65 | 65 | Multiples of 14 |
| 9 | Wheat, Rice, Maize, Barley, Cotton | Cotton | Cereal crops; cotton is a fibre crop |
| 10 | Square, Circle, Triangle, Sphere, Rectangle | Sphere | Flat shapes |
| 11 | AB, CD, EF, GH, IK | IK | Consecutive letters |
| 12 | BD, CE, DF, EG, FI | FI | Inner gap 2 (FI has gap 3) |
| 13 | 3, 8, 15, 24, 34 | 34 | n² − 1 (the next would be 35) |
| 14 | 100, 121, 144, 169, 200 | 200 | Perfect squares |
| 15 | January, March, May, June, July | June | 31 days; June has 30 |
Part 9 — A timed-practice routine
| Day | Task | Target |
|---|---|---|
| 1 | Learn the prime list, squares to 20 and cubes to 10 by writing them from memory | All lists perfect |
| 2 | 20 number sets, writing the rule beside each | 90 percent correct, no timer |
| 3 | 20 word sets, writing the family name for each | Name the family within 10 seconds |
| 4 | 15 letter and alpha-numeric sets with positions written | Positions written for every letter |
| 5 | Mixed set of 20 | 12 minutes, about 35 seconds each |
| 6 | Redo the wrong ones and write the correct rule beside each | No repeat mistakes |
| 7 | Timed mixed set of 20 and the 30 practice questions attached to this page | 10 minutes for the set |
Skip any set where two items still look odd after 30 seconds, and come back at the end.
One-line revision: identify the item type, find the property that four items share (prime, square, cube, divisibility, category, position gap), and the single item that breaks it is the answer.
Part 10 — Where this connects
Classification trains the same pattern-spotting that drives Analogy and Number & Letter Series. Its letter-position checks are the base of Coding-Decoding, and its category thinking returns in Syllogism and in figure form in Non-Verbal Reasoning.
Practice questions
Now test yourself. 8 free sample questions with explanations. 22 more in the timed practice test.
Q1. Three of the following words are alike. Find the one that is different.
▸ Show answer & explanation
Answer: D
Doctor, engineer and teacher are professions (people who work), whereas hospital is a place, so hospital is the odd one out.
Q2. Three of the following four geometric solids share a property and one does not. Choose the odd one out.
▸ Show answer & explanation
Answer: C
A cube, cuboid and pyramid are solids made up of flat polygonal faces, whereas a sphere has a single curved surface with no flat faces, so the sphere is the odd one out.
Q3. Choose the odd one out: $145, 150, 155, 162$
▸ Show answer & explanation
Answer: D
$145, 150$ and $155$ are all multiples of $5$ (they end in 0 or 5), but $162$ is not a multiple of $5$, so it is the odd one out.
Q4. Pick the odd one out from the following animals.
▸ Show answer & explanation
Answer: D
Snake, lizard and crocodile are reptiles, whereas a frog is an amphibian, so the frog is the odd one out.
Q5. Choose the odd one out: $111, 222, 333, 446$
▸ Show answer & explanation
Answer: D
In $111$, $222$ and $333$ all three digits are identical. In $446$ the digits are not all the same, so $446$ is the odd one out.
Q6. Pick the number that is different from the rest: $12, 18, 24, 26$
▸ Show answer & explanation
Answer: D
$12, 18$ and $24$ are all divisible by $6$, but $26$ is not divisible by $6$, so $26$ is the odd one out.
Q7. Three of the following are alike. Choose the one that does not belong to the group.
▸ Show answer & explanation
Answer: C
India, Japan and Egypt are countries in the continents of Asia and Africa, while Brazil is in South America. Among these, Brazil is the only South American country, so it is the odd one out.
Q8. Three of the following are alike in a certain way. Which one is different?
▸ Show answer & explanation
Answer: C
Guitar, violin and sitar are string instruments played by plucking or bowing strings, whereas a flute is a wind instrument, so the flute is the odd one out.
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