Introduction
Classification (Odd One Out) is a key reasoning topic in SSC CGL Tier-I. It tests your ability to identify the common property among a group of items and find the one that does not share it. Items can be numbers, letters, words, or figures. Mastery requires observation, pattern recognition, and logical deduction.
Number Classification
In number classification, you are given a set of numbers. Most share a common property (e.g., perfect squares, cubes, primes, divisibility, digit sum, etc.). You must find the number that does not fit. Often, the odd number is based on a different category or violates a pattern.
Key Points
- Check basic properties: prime/composite, even/odd, perfect square/cube, divisibility by a number.
- Look for digit-based patterns: sum of digits, product of digits, reverse, etc.
- Consider operations: addition, subtraction, multiplication, division among numbers.
- If numbers are large, check divisibility rules quickly.
Solved Example 1
Question: Find the odd one out: 121, 144, 169, 200
Solution: 200
Explanation: 121=11^2, 144=12^2, 169=13^2 are perfect squares. 200 is not a perfect square.
Letter and Word Classification
In letter classification, groups of letters are given, often based on alphabetical positions, vowels/consonants, or patterns like skipping letters. In word classification, words are related by meaning, category, or spelling. The odd one is the word that does not belong to the same category or does not follow the letter pattern.
Key Points
- Convert letters to their positions (A=1, B=2, etc.) to find numerical patterns.
- Check for vowels, consonants, or specific letter combinations.
- For words, identify the common category (e.g., fruits, animals, occupations) and find the unrelated one.
- Look for synonyms, antonyms, or homophones.
Solved Example 1
Question: Find the odd one out: Apple, Banana, Carrot, Mango
Solution: Carrot
Explanation: Apple, Banana, and Mango are fruits; Carrot is a vegetable.
Practice Questions
Q1. Find the odd one out: 3, 5, 7, 9, 11
Answer: 9
Explanation: 3, 5, 7, 11 are prime numbers; 9 is composite (3×3).
Q2. Find the odd one out: Dog, Cat, Lion, Cow
Answer: Lion
Explanation: Dog, Cat, and Cow are domestic animals; Lion is wild.
Q3. Find the odd one out: AB, CD, EF, GH, IJ, KL, MN, OP, QR, ST, UV, WX, YZ
Answer: No odd one out; all are pairs of consecutive letters.
Explanation: All given pairs are consecutive letters in the alphabet. However, if one pair is reversed (e.g., BA), that would be odd. Here, all are in order, so none is odd. (Note: In exams, usually one is different; here all are same.)
Common Mistakes
- Assuming a pattern too quickly without checking all possibilities. Always verify with all items.
- Ignoring multiple possible patterns; sometimes more than one odd one out seems possible, but only one fits the intended logic.
- Forgetting to consider alphabetical positions for letter-based questions.
- Overlooking simple categories like fruits, animals, etc., and searching for complex patterns.
Quick Revision
- Classification questions require finding the item that does not share the common property of the group.
- Common patterns: numerical (prime, square, cube, divisibility), alphabetical (position, vowels), semantic (category, meaning).
- Always check all options against the identified pattern to ensure uniqueness.
- Practice with mixed types: numbers, letters, words, and figures.