Basic Concepts: Classification

Introduction

• To 'classify' means to assign some particular characteristic to the various members/part of a group and identify them on the basis of those particular characteristics only.
• Classification questions aim to test the skills of a candidate in determining the features of various things and the candidate has to answer which one is odd-one from the group of 4 options. The odd-one option shouldn't possess the skill which must be common among the other three options. Such questions are really scoring as they require minimum calculations (if verbal). So, let's understand how to solve various types of 'Classification' questions.
• All we have to do is identify the common feature in the 3 options. There can be various types of patterns that can be found in Classification questions. 
• This common feature must be unique, ascertainable, and must not be present in the odd-one option. While solving these questions, one should have basic awareness about general knowledge including Science, Geography, History, Mathematics, etc.

Different Types of Questions asked in Competition Exams 

1. Finding the Odd-Word

• In such questions, four 'meaningful' words are given. These words can be found in the dictionary. Apart from that, these have a similar feature, based on that we're supposed to find the odd word.

Example:
(i) (a) Treachery
(b) Fraud
(c) Deceit
(d) Morbid

Here, we can see that all except Morbid are synonymous to each other as they all mean 'falsehood' while 'morbid' means 'diseased'. So, here we should have a good vocabulary to solve such questions.

(ii) (a) Feeling
(b) Joy
(c) Anxiety
(d) Anger

Here, Joy, Anxiety, and  Anger are all the types of Feeling. And, Feeling is a generic(or general) term. To solve this, we need a good knowledge of adjectives.

(iii) (a) Skull
(b) Appendix
(c) Pelvis
(d) Fibula

Here, All except Appendix are bones. While Appendix is an organ made of muscle. To solve this, we need a basic knowledge of science.

2. Finding the Odd-Pair of Words

• In such questions, four options are given. Each option has a pair of words (that can be found in the dictionary & hence meaningful).  Each of the three pairs depicts a relationship among each other and this relationship is common in all the four pairs but can't be found in the 4th odd-one pair. We're supposed to find that odd-pair that doesn't possess that common relationship.

Example:
(i) (a) Lion: Roar
(b) Snake: Hiss
(c) Frog: Bleat
(d)  Bees: hum

In all the pairs, the second word is the sound made by the animal, which is also the first word. But in the pair of frog: bleat, bleat is the sound made by sheep not frogs.

(ii) (a) Protein: Marasmus
(b) Sodium: Rickets
(c) Iodine: Goitre
(d) Iron: Anaemia

In all the pairs, the second word describes the diseases, caused by a deficiency of element, which is the first word. But in the pair of Sodium: Rickets, Rickets is being caused by the deficiency of Vitamin D, not Sodium.

(iii) (a) Valley: Depth
(b) Good: bad
(c) High: Low
(d) Black: white

Here, all the pairs contain the words which are antonym, i.e. they mean the opposite of each other. But, Valley & Depth are synonyms to each other.

3. Finding the Odd Number

• In such questions, four numbers are given. Each of the 3 numbers has common features like prime numbers or odd numbers, or all divisible by '7', while the 4th number isn't so we have to identify that odd number that doesn't have the feature the other numbers have.

Example
(i) (a) 145
(b) 197
(c) 257
(d) 399

Here, all the numbers except 399 are of the form (Square + 1)
i.e. 257 ⇒ 256 + 1.
But, 399 ⇒ 398 + 1 ⇒ 398 isn't the square of any number.

(ii) (a) 3759
(b) 2936
(c) 6927
(d) 4836

Here, in all the options the pattern depicted is like this:
i.e. 3759 ⇒ (7+9) = 2×(3+5) ⇒ 16 = 2 × 8.
But, 2936 isn't following this pattern: (2+6) ≠ 2×(2+3).

(iii) (a) 5698
(b) 4321
(c) 7963
(d) 4232

Here, '4232' is the only number where digits have been repeated while all other options have three different unique digits.

4. Finding the Odd-Pair of Numbers

• In such questions, four options are given. Each option has a pair of numbers. Each four pair depicts a relationship among each other and this relationship is common in all the three pairs but can't be found in the 4th odd-one pair. We're supposed to find that odd-pair that doesn't possess that common relationship.

Example
(i) (a) 140 - 45
(b) 110 - 35
(c) 100 - 30
(d) 80 - 25

The pattern seen here is (first number - 5) ÷3= Second number.
i.e. 140 - 45 ⇒ (140 - 5) ÷ 3 = 45.
But, 100 - 30 ⇒ (100 - 5) ÷ 3 ≠ 30

(ii) (a) 7: 26
(b) 8: 30
(c) 10: 35
(d) 13: 44

Here, the pattern is: 2nd number = (1st number × 3) + 5
i.e. 7: 26 ⇒ 26 = 7 × 3 + 5 = 26
But in case 8: 30 ⇒ 30 ≠ 8×3 + 5

(iii) (a) 21 - 49
(b) 24 - 64
(c) 25 - 54
(d) 81 - 36

21 & 49 have 7 as common factor, 24 & 64 have 8 as common factor. 81 & 36 have 9 as a common factor while 25 & 54 have no common factor.

5. Finding the Odd Letters

• In such types of questions, four options contain a random group of letters. These random groups of letters have a common pattern, and this pattern is common in all three options, but can't be found in the 4th odd-one. We're supposed to find that odd-one that doesn't possess that common pattern.

Example
(i) (a) DECB
(b) GDFE
(c) HKIJ
(d) JFHG

All except JFHG contain consecutive alphabets in random order.

(ii) (a) ACZX
(b) BDYW
(c) EGVT
(d) CEUS

In all the groups except CEUS, 1st and 3rd letters occupy the same position from the beginning & end of alphabetical series respectively.