Classification Notes for SSC Exams

Classification, also called odd one out, is a Reasoning topic in which a group of words, letters or numbers is given and you have to find the one that does not belong to the group. Four items share a common property, and one item does not. Classification questions are asked in almost every SSC Reasoning paper, and they are quick marks once you learn the common categories. These classification notes for SSC explain word, letter-cluster and number classification with tables, shortcuts, solved examples and practice questions.

What Is Classification?

• You are given four or five items, and one of them is different from the rest.
• The difference may be in meaning, category, pattern, property or a mathematical rule.
• The task is to find the common property of the group first, and then pick the item that breaks it.
• Classification questions can be on words, letters, letter clusters, numbers or number pairs.

Step-by-Step Method

1. Read all the options once and look for the most obvious common property.
2. Check whether three or four items belong to one category, such as birds, rivers or tools.
3. Find the item that does not fit that category.
4. If no category is clear, check the second level, such as the type of food, the state or the use.
5. For numbers and letters, test the rules in the tables below before deciding.

Word Classification: Common Categories

Common categories to remember: mammals, birds, reptiles, fish, insects, fruits, vegetables, flowers, metals, planets, rivers, mountains, cities, states, languages, professions, tools, vehicles, body organs and festivals.

Number Classification: Rules to Check

Letter-Cluster Classification

In this type, groups of letters are given. Convert each letter to its position and check the gap between the letters.

• Same gap inside each group: in ABC, DEF, GHI, JKM, the first three groups have consecutive letters, but JKM breaks the pattern, so JKM is odd.
• Gap of two: in BDF, HJL, NPR, TVW, the expected last group is TVX, so TVW is odd.
• Wrap-around: in PQR, STU, VWX, YZB, the last group should be YZA, so YZB is odd.
• Mirror pairs: if every group has letters whose positions add to 27, find the group that does not.

Example 1. Find the odd one: CF, GJ, KN, OQ.
The gap inside the first three pairs is 3 (C to F, G to J, K to N), but O to Q has a gap of 2. Odd one: OQ.

More Solved Examples

Example 2. Find the odd one: Ganga, Yamuna, Godavari, Himalaya.
Ganga, Yamuna and Godavari are rivers, while Himalaya is a mountain range. Answer: Himalaya.

Example 3. Find the odd number: 144, 169, 196, 225, 250.
144 = 12², 169 = 13², 196 = 14², 225 = 15², but 250 is not a perfect square. Answer: 250.

Example 4. Find the odd one: Cricket, Hockey, Chess, Football.
Cricket, hockey and football are outdoor team sports. Chess is an indoor board game. Answer: Chess.

Quick Tips

• Do not stop at the first common property. Check whether another group also forms, and choose the strongest one.
• If the words seem unrelated, think about their category, use, origin or number of letters.
• For numbers, test prime, square, cube and multiples first, and then the digit sum.
• For letter clusters, write the positions of the letters below them.
• If two items seem odd, the group is usually based on a stricter rule. Look for it again.

Quick Revision Points

• Classification means finding the item that does not belong.
• First find the common property, then pick the exception.
• Test prime, square, cube and multiples in number questions.
• For letter clusters, compare the gaps between letters.
• Revise common categories of animals, plants, metals and places.

Practice Questions With Answers

1. Copper, Iron, Zinc, Coal. Find the odd one.
   Answer: Coal (the rest are metals).
2. Mercury, Venus, Moon, Mars. Find the odd one.
   Answer: Moon (a satellite, not a planet).
3. 2, 3, 5, 7, 9. Find the odd number.
   Answer: 9 (not prime).
4. 144, 169, 196, 225, 250. Find the odd number.
   Answer: 250 (not a perfect square).
5. PQR, STU, VWX, YZB. Find the odd group.
   Answer: YZB (it should be YZA).
6. Ganga, Yamuna, Godavari, Himalaya. Find the odd one.
   Answer: Himalaya (a mountain range).
7. Whale, Shark, Dolphin, Seal. Find the odd one.
   Answer: Shark (a fish, the rest are mammals).
8. 15, 25, 35, 45, 52. Find the odd number.
   Answer: 52 (the rest are multiples of 5).
9. Square, Rectangle, Circle, Pyramid. Find the odd one.
   Answer: Pyramid (three-dimensional).
10. Cricket, Hockey, Chess, Football. Find the odd one.
    Answer: Chess (an indoor board game).

How to Practise This Chapter

Solve ten classification questions daily and always write the common property of the group. Then try timed sets in our practice papers and check the real exam pattern on the previous year papers page. Read Analogy before this chapter and Blood Relations after it.

Explore More SSC Subjects

SSC exams test many subjects, so connect this topic with the related subjects below:

• Quantitative Aptitude Notes
• English Notes
• General Awareness Notes
• Computer Knowledge Notes
• Stenography Notes
• All SSC subjects and notes

Frequently Asked Questions

What is classification in reasoning?

Classification is a reasoning topic in which a group of words, letters or numbers is given, and you have to find the one that does not share the common property of the others.

Is classification the same as odd one out?

Yes. Classification and odd one out mean the same thing in the SSC Reasoning syllabus. Both ask you to find the item that is different from the rest.

How many classification questions come in SSC exams?

Usually two to four classification questions come in the Reasoning section of SSC Tier 1 papers, although the exact number changes from year to year.

What is the best way to solve word classification?

Find the category to which most words belong, such as birds, rivers or metals, and choose the word that does not fit. If the category is unclear, check use, origin or type.

How do I solve number classification?

Test the numbers for prime, perfect square, perfect cube, multiples of a number and digit sum. The rule that fits four numbers but not the fifth gives the answer.

How do I solve letter-cluster classification?

Convert each letter into its position and compare the gaps between the letters in every group. The group that has a different gap or a different order is the odd one.

What if two options look like the odd one?

Look for a stricter rule that groups the other three items together. For example, if two items are birds but only one cannot fly, check which rule matches the remaining items.

Do I need general knowledge for classification?

For word classification, basic general knowledge helps, such as the classification of animals, metals and planets. Number and letter classification need only reasoning.

How can I improve speed in classification?

Revise the common categories, practise ten questions daily and learn the number rules from the table. Classification should take about 15 to 20 seconds per question.

Are number pair classification questions difficult?

No. In these questions, find the relation inside each pair, such as square or double, and look for the pair that does not follow it.

Why do I get classification questions wrong?

The most common reasons are choosing the first pattern you see, ignoring a stricter rule, and not checking all the options before answering.

Is there any shortcut for classification questions?

The shortcut is elimination. Find any two items that clearly belong together, then see which other items share that property, and the remaining item is the odd one.

Are classification questions asked in Hindi medium papers?

Yes. The same types of questions are asked in Hindi medium papers, with words in Hindi and numbers and letters in the same form.