Odd One Out / Classification: Complete Reasoning Module
Learn to find the common property of a group and spot the item that does not belong. Concepts, a step-by-step method, 28 solved MCQs and a timed mock test.
- 4 Question Types
- 28 Solved MCQs
- 20-Question Timed Test
Subtopics covered
- Number Odd One Out
- Letter Odd One Out
- Number Odd One Out (Brackets / Set Type)
- Words Odd One Out
Concept explanation
In an odd one out (classification) question, a group of items shares one common property and a single item does not follow it. Your job is to discover the shared property and pick the item that breaks it.
Step 1. Number odd one out
Numbers share a property such as being a square, cube, prime, multiple of a number, or having a certain digit sum.
Step 2. Letter odd one out
Letters (or letter groups) share a gap, a direction, a vowel count or a position sum. Convert letters to positions (A = 1 … Z = 26) to check.
Step 3. Brackets / set type
Each bracket follows one rule across its numbers. Three sets obey it and one does not. Test the rule on the clearest sets first.
Step 4. Words odd one out
Words belong to a common category such as fruits, tools, planets, mammals or metals. One word belongs to a different category.
Procedure to solve the problem
- Identify the type. Numbers, letters, bracket sets or words?
- Compare two items first. Look for what they share.
- Name the property. Write it in one line, such as “perfect squares” or “third = first + second”.
- Test it on a third item. A real property must work for all but one item.
- Pick the item that fails. That is the odd one out.
- Double-check. If two items seem to fail, your property is wrong. Look for a different one.
| Type | Common properties to test |
|---|---|
| Number | Squares, cubes, primes, multiples, n²±1, divisibility by 3 or 9, digit sum |
| Letter | Fixed gap, consecutive letters, direction (forward or backward), vowel count, position sum 27 |
| Set | Sum, product, a²+b², (a+b)², a²−b², division, powers |
| Word | Category, function, living or non-living, plant or animal, material, place |
Solved MCQs (7 per type, basic to advanced)
Tap an option to see whether it is right or wrong. Open the Explanation tab under any question to see the full reasoning.
Number Odd One Out
Q1. Find the odd one out.
Select an option to see if it is right or wrong.
Answer: D. 30. 9, 16 and 25 are perfect squares (3², 4², 5²). 30 is not a perfect square.
Q2. Find the odd one out.
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Answer: A. 27. 17, 19 and 23 are prime numbers. 27 = 3 × 9, so it is composite.
Q3. Find the odd one out.
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Answer: C. 100. 8, 27 and 64 are perfect cubes (2³, 3³, 4³). 100 is a perfect square, not a cube.
Q4. Find the odd one out.
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Answer: B. 35. 12, 18 and 24 are multiples of 6. 35 is not divisible by 6.
Q5. Find the odd one out.
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Answer: D. 50. 15, 24 and 35 follow n² − 1 (4² − 1, 5² − 1, 6² − 1). 50 equals 7² + 1, so it breaks the pattern.
Q6. Find the odd one out.
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Answer: A. 464. The digit sums of 156, 273 and 381 are all 12, so each is divisible by 3. The digit sum of 464 is 14, so it is not divisible by 3.
Q7. Find the odd one out.
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Answer: C. 331. 143 = 11 × 13, 221 = 13 × 17 and 323 = 17 × 19, each a product of two primes. 331 is itself a prime number.
Letter Odd One Out
Q1. Find the odd one out.
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Answer: D. K. A, E and I are vowels. K is a consonant.
Q2. Find the odd one out.
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Answer: B. NQ. In BD, FH and JL the second letter is 2 places after the first. In NQ it is 3 places after (N, O, P, Q).
Q3. Find the odd one out.
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Answer: C. RTW. ACE, GIK and MOQ move forward by 2 each time. RTW moves +2 and then +3.
Q4. Find the odd one out.
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Answer: A. DV. In AZ, BY and CX the two letter positions add up to 27 (1 + 26, 2 + 25, 3 + 24). D (4) + V (22) = 26.
Q5. Find the odd one out.
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Answer: D. OPQ. ZYX, WVU and TSR run backwards through the alphabet. OPQ runs forwards.
Q6. Find the odd one out.
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Answer: B. NOQ. BCD, FGH and JKL are three consecutive letters. NOQ skips P, so it is not consecutive.
Q7. Find the odd one out.
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Answer: C. FIST. PEAK, TOUR and ROAD each contain exactly two vowels. FIST has only one vowel (I).
Number Odd One Out (Brackets / Set Type)
Q1. Find the odd set.
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Answer: C. (7, 8, 16). In the other sets the third number is the sum of the first two (3 + 4 = 7, 5 + 6 = 11, 9 + 10 = 19). Here 7 + 8 = 15, not 16.
Q2. Find the odd set.
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Answer: A. (5, 6, 32). In the other sets the third number is the product of the first two. Here 5 × 6 = 30, not 32.
Q3. Find the odd set.
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Answer: D. (7, 49, 57). The third number is n + n² (4 + 16, 5 + 25, 6 + 36). Here 7 + 49 = 56, not 57.
Q4. Find the odd set.
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Answer: B. (5, 6, 60). The third number is a² + b² (4 + 9, 9 + 16, 16 + 25). Here 25 + 36 = 61, not 60.
Q5. Find the odd set.
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Answer: C. (4, 5, 80). The third number is (a + b)²: 3² = 9, 5² = 25, 7² = 49. Here (4 + 5)² = 81, not 80.
Q6. Find the odd set.
Select an option to see if it is right or wrong.
Answer: D. (7, 24, 26). The third number is the hypotenuse: 3² + 4² = 5², 5² + 12² = 13², 8² + 15² = 17². For (7, 24) the sum is 49 + 576 = 625 = 25², so the third should be 25, not 26.
Q7. Find the odd set.
Select an option to see if it is right or wrong.
Answer: A. (10, 6, 65). The third number is a² − b² (25 − 9, 49 − 16, 81 − 25). Here 100 − 36 = 64, not 65.
Words Odd One Out
Q1. Find the odd one out.
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Answer: D. Carrot. Apple, mango and banana are fruits. Carrot is a vegetable.
Q2. Find the odd one out.
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Answer: B. Hammer. Table, chair and sofa are furniture. A hammer is a tool.
Q3. Find the odd one out.
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Answer: C. Cow. Lion, tiger and leopard are wild, meat-eating big cats. A cow is a domestic, plant-eating animal.
Q4. Find the odd one out.
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Answer: A. Moon. Mercury, Venus and Mars are planets. The Moon is a natural satellite.
Q5. Find the odd one out.
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Answer: D. Bronze. Oxygen, nitrogen and hydrogen are elements. Bronze is an alloy of copper and tin.
Q6. Find the odd one out.
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Answer: B. Chess. Hockey, cricket and football are outdoor team games played on a field. Chess is a two-player board game.
Q7. Find the odd one out.
Select an option to see if it is right or wrong.
Answer: C. Penguin. Bat, whale and dolphin are mammals. A penguin is a bird.
Timed practice test
| Questions | 20 (picked at random from a pool of 24) |
|---|---|
| Time allowed | 20 minutes |
| Marking | 1 mark per correct answer, no negative marking |
| Tools | Mark for review and a jump-to-question panel |
| Name | Required before starting. Letters only, no numbers |
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