Reasoning

Classification Guide & Practice

Q: Four of the following five are alike in a certain way and so form a group. Which is the one that does not belong to that group? (1) Crow (2) Vulture (...

1. Analyze the biological properties of each option: * *Crow, Vulture, Ostrich, and Eagle* belong to the biological class Aves (Birds). They possess feathers, beaks, and lay eggs. * *Bat* belongs to the class Mammalia (Mammals). It gives birth to live young ones and feeds them milk. 2. Therefore, Bat is the odd one out because it is the only mammal in the group. Answer: (3) Bat

Q: Four number-pairs have been given, out of which three are alike in some manner and one is different. Select the number-pair that is different from the...

1. Identify the relationship between the fractions ($x/y$) and the single integers ($z$): Test the sum of squares of the numerator ($x$) and denominator ($y$) against the integer value $z$ ($x^2 + y^2 = z$). 2. Calculate for each option: * Option (b): $7^2 + 3^2 = 49 + 9 = 58$. (Matches) * Option (c): $18^2 + 9^2 = 324 + 81 = 405$. (Matches) * Option (d): $5^2 + 6^2 = 25 + 36 = 61$. (Matches) * Option (a): $12^2 + 21^2 = 144 + 441 = 585 \neq 565$. (Does not match) 3. Since option (a) does not satisfy the formula $x^2 + y^2 = z$, it is the odd one out. Answer: (a) 12/21, 565

Q: Four letter-clusters have been given, out of which three are alike in some manner and one is different. Select the odd letter-cluster. (a) ADHK (b) FI...

1. Convert each letter to its positional value in the English alphabet ($A=1, B=2, \dots, Z=26$): * $ADHK \to [1, 4, 8, 11]$ * $FIMP \to [6, 9, 13, 16]$ * $PSVZ \to [16, 19, 22, 26]$ * $ZCGJ \to [26, 3, 7, 10]$ 2. Analyze the difference patterns between consecutive letters in each group: * Cluster (a) $ADHK$: * $4 - 1 = +3$ * $8 - 4 = +4$ * $11 - 8 = +3$ * *Difference pattern:* $(+3, +4, +3)$ * Cluster (b) $FIMP$: * $9 - 6 = +3$ * $13 - 9 = +4$ * $16 - 13 = +3$ * *Difference pattern:* $(+3, +4, +3)$ * Cluster (c) $PSVZ$: * $19 - 16 = +3$ * $22 - 19 = +3$ * $26 - 22 = +4$ * *Difference pattern:* $(+3, +3, +4)$ * Cluster (d) $ZCGJ$: * $3 - 26 \equiv 29 - 26 = +3$ (since $C$ is 3rd letter, wrapping around Z) * $7 - 3 = +4$ * $10 - 7 = +3$ * *Difference pattern:* $(+3, +4, +3)$ 3. Compare the difference patterns: Clusters (a), (b), and (d) all follow the step sequence of $(+3, +4, +3)$. Cluster (c) follows the step sequence of $(+3, +3, +4)$. 4. Therefore, $PSVZ$ is the odd letter-cluster. Answer: (c) PSVZ

Practice word, number, and letter classification (odd one out) questions with pattern recognition tricks and free SSC/Banking mock tests. Explore dynamic solver blueprints, master fundamental equations, examine step-by-step solved examples, and practice with real exam-grade mock test sets.

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Practice Question Papers

15 min

Easy

1. Fundamentals & Definitions

Definition of Classification

Classification literally means 'to group'. It is the process of assorting a given set of items (words, letters, numbers, or pairs) into a single class or category on the basis of a common quality, property, logical rule, or relationship. The item that does not conform to this shared characteristic is identified as the "Odd One Out".

Key Terminology

Target Group / Class: A set of elements that share a defined common attribute.
Odd One Out: The single element in a given selection that does not fit the common logical rule of the group.
Basis of Classification: The underlying criteria or rule (e.g., mathematical operations, grammatical category, scientific taxonomy) used to relate the other elements.

Types of Classification Questions

Word Classification: Identifying the word that differs semantically, grammatically, or taxonomically from the others in the group.
Letter / Alphabet Classification: Finding the odd letter cluster based on alphabetical positions, vowel/consonant distribution, or opposite-letter relationships.
Number Classification: Finding the odd number, pair, or group based on arithmetic properties, divisibility, algebraic formulas, or digit manipulations.

2. Core Concepts & Formulas

Word Classification (Semantic Relationships)

Word classification relies on real-world knowledge across biology, geography, physics, grammar, and economics.

Relationship Sub-Concept	Explanation	Group Characteristics	Example
Biological Class / Taxonomy	Distinguishing animals based on mammal, avian, reptile, or amphibian classes.	Mammals vs. Birds (Aves)	Bat (mammal; others like Crow, Sparrow, Pigeon are birds).
Animal and Sound	Associating an animal with its specific vocalization.	Animal - Vocalization	Cocks - Croak (cocks crow; frogs croak).
Animal and Offspring	Associating an animal with its young one.	Animal - Young One	Baboon - Pup (baboons have infants; pups belong to dogs/seals).
Geographical Parameters	Distinguishing locations by rivers, capitals, power stations, or functions.	Cities on River Ganga	Mathura (on Yamuna; Kanpur, Varanasi, Haridwar are on Ganga).
Product Utility / Economics	Grouping goods by demand relationships.	Complementary Goods vs. Substitutes	Tea - Coffee (substitutes; Shoes-Polish, Car-Petrol are complementary).
Anatomy & Pathology	Differentiating bones, organs, or disease types.	Deficiency Diseases vs. Hormonal	Cretinism (hormonal; Kwashiorkor, Goitre, Marasmus are deficiency).
Grammatical Function	Classifying words by parts of speech.	Conjunctions vs. Adverbs	Again (adverb; Unless, While, But are conjunctions).
Physical Quantities	Classifying variables in classical mechanics.	Vector vs. Scalar quantities	Energy (scalar; Momentum, Acceleration, Force are vectors).

Letter Classification (Alphabetical Patterns)

Letter patterns are analyzed using numerical positions in the English alphabet ( $A = 1, B = 2, \dots, Z = 26$ ) and opposite-letter pairs.

Alphabet Positional Reference Table

Letter	Pos	Letter	Pos	Letter	Pos	Letter	Pos	Letter	Pos
A	1	F	6	K	11	P	16	U	21
B	2	G	7	L	12	Q	17	V	22
C	3	H	8	M	13	R	18	W	23
D	4	I	9	N	14	S	19	X	24
E	5	J	10	O	15	T	20	Y	25
Z	26

Opposite Letters (Sum of positions = 27)

Opposite letter pairs represent letters at equal distances from the start and end of the alphabet.

Letter	Value	Opposite	Value	Memory Aid
A	1	Z	26	AtoZ
B	2	Y	25	Boy
C	3	X	24	Crux
D	4	W	23	Dew
E	5	V	22	Eve
F	6	U	21	Full
G	7	T	20	GT Road
H	8	S	19	High School
I	9	R	18	Indian Railways
J	10	Q	17	Jack-Queen
K	11	P	16	Kanpur
L	12	O	15	Love
M	13	N	14	Man

Common Letter Clusters Rules

Constant Positional Gaps: Differences between consecutive letters are identical (e.g., $+3, +4, +3$ offset).
Vowel-Consonant Distribution: Sorting clusters by vowel count or the index of vowels (e.g., middle letter must be a vowel).
Reverse-Letter Pairing: The cluster consists of two pairs of opposite letters (e.g., $LO$ and $PK$ are opposites in $LOPK$ ).
Unjumbled Word Semantics: Anagrams that must be solved before classification (e.g., unjumbling letters to reveal planet names vs. metal names).

Number Classification (Numerical Properties)

Numerical patterns follow specific mathematical formulas, series trends, or digital operations.

Mathematical Category	Formula / Logical Rule	Example Options	Odd One Out Logic
Perfect Squares & Cubes	$x = k^2$ or $x = k^3$	121, 137, 153, 177, 183	121 (Only perfect square: $11^2$ ).
Square/Cube Offset	$x = k^2 \pm c$ or $x = k^3 \pm c$	226, 290, 170, 122, 360	360 (Others are $k^2 + 1$ : $15^2+1, 17^2+1, 13^2+1, 11^2+1$ ).
Variable Polynomial Trend	$x = n^2 - n$ or $x = n^2 + n$	72, 42, 110, 156, 152	152 (Others follow $n^2 - n$ : $9^2-9, 7^2-7, 11^2-11, 13^2-13$ ).
Exponent Series	$x = 2^n + 1$	5, 9, 17, 33, 7	7 (Others are $2^2+1, 2^3+1, 2^4+1, 2^5+1$ ).
Factorial Series	$x = n!$	120, 720, 5040, 40320, 52480	52480 (Others are factorials of 5, 6, 7, 8).
Digital Operations	Sum of digits equals a constant $C$	721, 910, 811, 651	651 (Sums to 12; others sum to 10).
Pair Difference	$y - x = C$	(62-37), (85-60), (103-78), (74-40)	(74-40) (Difference is 34; others have a difference of 25).
Pair Multiplicative Shift	$y = m \cdot x + c$	(7-18), (9-26), (11-36), (13-42)	(11-36) (Others follow $y = 4x - 10$ ).
Cross-Digit Arithmetic	$z = x^2 + y^2$ (for format $x/y, z$ )	(7/3, 58), (18/9, 405), (12/21, 565)	(12/21, 565) (as $12^2 + 21^2 = 585 \neq 565$ ).
Digit Positional Reversal	$y$ is the reversed digit form of $x$	(27:72), (34:43), (65:56), (42:52)	(42:52) (Digits are not reversed).

Typical Exam Weightage

Exam	Typical Questions
SSC (CGL / CHSL / MTS)	2–3 questions
Banking (IBPS / SBI)	1–2 questions
Railways (RRB)	1–2 questions

Also called "odd one out" — usually the quickest-scoring reasoning question type when it appears.

Figures are typical ranges based on recent-year patterns, not a guarantee for any specific upcoming paper — always cross-check against the latest official syllabus and previous-year papers for Classification.

Solved Examples

1Example 1: Easy (Word Classification)

Question: Four of the following five are alike in a certain way and so form a group. Which is the one that does not belong to that group? (1) Crow (2) Vulture (3) Bat (4) Ostrich (5) Eagle

View Detailed Solution & Explanation

Step-by-Step Explanation

Analyze the biological properties of each option:
- Crow, Vulture, Ostrich, and Eagle belong to the biological class Aves (Birds). They possess feathers, beaks, and lay eggs.
- Bat belongs to the class Mammalia (Mammals). It gives birth to live young ones and feeds them milk.
Therefore, Bat is the odd one out because it is the only mammal in the group. Answer: (3) Bat

2Example 2: Moderate (Number Classification)

Question: Four number-pairs have been given, out of which three are alike in some manner and one is different. Select the number-pair that is different from the rest. (a) 12/21, 565 (b) 7/3, 58 (c) 18/9, 405 (d) 5/6, 61

View Detailed Solution & Explanation

Step-by-Step Explanation

Identify the relationship between the fractions ( $x/y$ ) and the single integers ( $z$ ): Test the sum of squares of the numerator ( $x$ ) and denominator ( $y$ ) against the integer value $z$ ( $x^2 + y^2 = z$ ).
Calculate for each option:
- Option (b): $7^2 + 3^2 = 49 + 9 = 58$ . (Matches)
- Option (c): $18^2 + 9^2 = 324 + 81 = 405$ . (Matches)
- Option (d): $5^2 + 6^2 = 25 + 36 = 61$ . (Matches)
- Option (a): $12^2 + 21^2 = 144 + 441 = 585 \neq 565$ . (Does not match)
Since option (a) does not satisfy the formula $x^2 + y^2 = z$ , it is the odd one out. Answer: (a) 12/21, 565

3Example 3: Hard (Letter Classification)

Question: Four letter-clusters have been given, out of which three are alike in some manner and one is different. Select the odd letter-cluster. (a) ADHK (b) FIMP (c) PSVZ (d) ZCGJ

View Detailed Solution & Explanation

Step-by-Step Explanation

Convert each letter to its positional value in the English alphabet ( $A=1, B=2, \dots, Z=26$ ):
- $ADHK \to [1, 4, 8, 11]$
- $FIMP \to [6, 9, 13, 16]$
- $PSVZ \to [16, 19, 22, 26]$
- $ZCGJ \to [26, 3, 7, 10]$
Analyze the difference patterns between consecutive letters in each group:
- Cluster (a) $ADHK$ :
  - $4 - 1 = +3$
  - $8 - 4 = +4$
  - $11 - 8 = +3$
  - Difference pattern: $(+3, +4, +3)$
- Cluster (b) $FIMP$ :
  - $9 - 6 = +3$
  - $13 - 9 = +4$
  - $16 - 13 = +3$
  - Difference pattern: $(+3, +4, +3)$
- Cluster (c) $PSVZ$ :
  - $19 - 16 = +3$
  - $22 - 19 = +3$
  - $26 - 22 = +4$
  - Difference pattern: $(+3, +3, +4)$
- Cluster (d) $ZCGJ$ :
  - $3 - 26 \equiv 29 - 26 = +3$ (since $C$ is 3rd letter, wrapping around Z)
  - $7 - 3 = +4$
  - $10 - 7 = +3$
  - Difference pattern: $(+3, +4, +3)$
Compare the difference patterns: Clusters (a), (b), and (d) all follow the step sequence of $(+3, +4, +3)$ . Cluster (c) follows the step sequence of $(+3, +3, +4)$ .
Therefore, $PSVZ$ is the odd letter-cluster. Answer: (c) PSVZ

Letter	Pos	Letter	Pos	Letter	Pos	Letter	Pos	Letter	Pos
A	1	F	6	K	11	P	16	U	21
B	2	G	7	L	12	Q	17	V	22
C	3	H	8	M	13	R	18	W	23
D	4	I	9	N	14	S	19	X	24
E	5	J	10	O	15	T	20	Y	25
Z	26

Letter	Pos	Letter	Pos	Letter	Pos	Letter	Pos	Letter	Pos
A	1	F	6	K	11	P	16	U	21
B	2	G	7	L	12	Q	17	V	22
C	3	H	8	M	13	R	18	W	23
D	4	I	9	N	14	S	19	X	24
E	5	J	10	O	15	T	20	Y	25
Z	26

Letter	Pos	Letter	Pos	Letter	Pos	Letter	Pos	Letter	Pos
A	1	F	6	K	11	P	16	U	21
B	2	G	7	L	12	Q	17	V	22
C	3	H	8	M	13	R	18	W	23
D	4	I	9	N	14	S	19	X	24
E	5	J	10	O	15	T	20	Y	25
Z	26