Classification - Logical Reasoning for CLAT PDF Download

Classification

The process of classification in logical-reasoning questions requires grouping items that share a common property and identifying the item that does not belong - the odd one out. Such questions test the candidate's ability to detect patterns based on alphabetic order, positional movement, semantic categories (general knowledge), numerical properties and other relations. The usual approach is: observe the common trait in four items, formulate the rule, and then check which item violates that rule.

TYPE - I

These questions involve groups of letters where the pattern is determined by the relative distances between successive letters in the English alphabet. The letters in each group follow a fixed step (forward or backward) except for the odd group. To solve: map each letter to its alphabetical index, compute differences between successive letters, and compare patterns across the options.

Three of the following four are alike on the basis of their position in English alphabet. Which is the one that does not belong to the group?

Example 1: 

(a) WZT    (b) KNH    (c) RUQ    (d) DGA

The correct answer is option (c)

Solution: In WZT, KNH and DGA the transition from the first to the second letter increases by 3 and the transition from second to third letter decreases by 6 in alphabetical order. In RUQ the second shift is -4 instead of -6, so it breaks the pattern.

Example 2: 

(a) CFI    (b) UXA    (c) RUX    (d) SVZ

The correct answer is (d)

Solution: In options (a), (b) and (c) the letters proceed with a constant forward step between successive letters (for example, option (a): C→F (+3), F→I (+3)). Option (d) does not maintain the same constant step pattern as the others, so it is the odd one.

Example 3: 

(a) WHITE-IWEHT    (b) BLACK-ABKLC    (c) TYPES-PTSYE    (d) ABOUT-OATUB

The correct answer is option (d)

Solution: In (a), (b) and (c) the letters are rearranged according to the same positional pattern, but in ABOUT → OATUB the second letter is placed in a different position, breaking the pattern.

TYPE - II

These questions are essentially category-based or semantic classification problems. Items are grouped by a shared general-knowledge property (e.g., planets vs satellites, forms of literature, parts of body). The same item can sometimes be grouped differently depending on the context, so it is important to fix the most natural or obvious category suggested by the set.

Three of the following four are alike in a certain way and so form a group. Which is the one that does not belong to that group?

Example 4:

(a) Earth    (b) Saturn    (c) Neptune    (d) Sun

The correct option is (d)

Solution: Earth, Saturn and Neptune are planets. Sun is a star, hence the odd one out.

Example 5:

(a) Earth    (b) Saturn    (c) Moon    (d) Mars

The correct option is (c)

Solution: Earth, Saturn and Mars are planets. Moon is a satellite, hence the odd one out.

Example 6:

(a) Novel    (b) Poetry    (c) Drama    (d) Literature

The correct option is (d)

Solution: Novel, Poetry and Drama are specific forms or genres within literature. "Literature" is the broader category that includes the other three; therefore it is the odd one when the criterion is a specific form.

Example 7:

(a) Gums    (b) Arm    (c) Hand    (d) Tears

The correct option is (d)

Solution: Gums, Arm and Hand are parts of the human body. Tears are a secretion and not a body part; therefore it is the odd one out.

TYPE - III

These questions use numerical analogy. One item differs in its numerical property while the other four share a common property. Common numerical properties used are:

• Prime numbers
• Divisibility by a fixed integer (e.g., 3, 9)
• Rational vs irrational
• Perfect squares, cubes or other power forms

Identify the shared numerical property among four options and then find the number that does not satisfy it.

Three of the following four are alike in a certain way and so form a group. Which is the one that does not belong to that group?

Example 8:

(a) 21    (b) 51    (c) 63    (d) 23

The correct option is (d)

Solution:

23 is a prime number and therefore not divisible by 3.

21 = 3 × 7

51 = 3 × 17

63 = 3 × 21

Therefore 21, 51 and 63 are all multiples of 3; 23 is not, so it is the odd one out.

Example 9:

(a) 117    (b) 74    (c) 153    (d) 108

The correct option is (b)

Solution:

Check divisibility by 3 and 9 for each number.

1. Divisibility Rule for 3

A number is divisible by 3 if the sum of its digits is a multiple of 3 (i.e., the sum is divisible by 3).

2. Divisibility Rule for 9

A number is divisible by 9 if the sum of its digits is a multiple of 9.

Therefore 117, 153 and 108 share divisibility by 3 (indeed by 9), while 74 does not, so 74 is the odd one out.

Strategy and Tips

• Always convert alphabetic options to positional numbers (A=1, B=2, ... Z=26) for letter-pattern questions and compute successive differences.
• For rearrangement or encoding problems, trace the positional mapping (which original index goes to which new index) and test consistency across options.
• In semantic/grouping problems, prefer the most natural, commonly accepted category (e.g., planet vs satellite, parts of speech, genres of literature) unless the option set clearly indicates a different grouping.
• For numerical items, test small standard properties first: divisibility by small primes (2,3,5), primality, perfect squares/cubes, parity (odd/even).
• If two plausible groupings exist, check which grouping isolates a single clear odd item without forcing uncommon interpretations.

Summary

Classification (odd-one-out) questions require identifying the common property shared by most options and locating the exception. Typical types include letter-patterns, semantic categories, and numerical properties. Systematic conversion (letters → positions, numbers → factors), careful checking of positional mappings, and application of basic GK or arithmetic rules will reliably lead to the correct choice.