Best explanation to understand and solve the odd man out series

This topic is one of the interesting and easy ones which involves all the other topics like NUMBERS, A.P, G.P, SQUARE ROOT, AND CUBE ROOT, etc.

Being logical is one of the important skills to solve of aptitude questions. Your perception to solve these problems should be unique and different.

Different problem related to different topics like numbers, alphabets, metals, cubes and squares will be asked in this section. So every problem will have different rules. 

We have given some important tips and tricks to solve these kind of problems.

Only thing you have to do is to understand the question clearly and think logically before answering the question.

We also have some set of aptitude questions based on this topic which will help you to practice for your exams. Take up our tests and score high.

What is a series?

The element or term that follows a definite rule or law is called a series. It has a sequence but cannot be generalised. 

Before answering the aptitude questions, find out what kind of series it is so that you can find the correct answer.

Different questions may have different kind of series like addition, subtraction, multiplication, division, transposition, etc.

Tips and Tricks

You may have questions based on the following categories.

1. Odd number/Even number/Prime numbers

This series may consist of odd numbers or even numbers or prime numbers except for that one number, which will be the odd man out that you have to find.

Hence, before solving the problems in this topic you must revise all basic topics in the numerical aptitude. 

2. Perfect squares/Cubes

Squares: 9, 16, 49, 81 ….

Cubes: 27, 64, 125, 216 …. 

The question will have any three numbers from cubes or square except one number which you have to find as odd man out.

3. Multiple of numbers

The series contains numbers which are multiples of different numbers. 

Example: 4, 8, 12, 16, 20 and so on.

So you have to find the odd man out which is not a multiple of that particular number. 

4. Numbers in A.P./G.P.

Geometric progression: x, xr, xr3, xr4

Arithmetic progression: x, x + y, x + 2y, x + 3y are said to be in A.P. 

The terms in series are arithmetic or geometric progression. 

5. Difference or sum of numbers

The difference between two consecutive numbers may increase or decrease

6. Cumulative series

In this type, the third number is the sum of the previous two numbers.

Example: 2, 4, 6, 10, 16, 26 and so on. So the answer will be the number which is out of this series.

7. Power series

In these types of series, the terms are defined on the basis of powers of numbers. The  number may be expressed in the form of n3 – n.


If n = 4, n3 – n = 60

If n = 5, n3 – n = 120…

Series: 60, 120, 210, 336 …

8. The middle digit is the sum of other two digits. 

Example: 165, 121, 363, etc

So you have to find the number whose middle digit is not the sum of other two number. That will be the odd man out. 

9. The series of numbers may follow different sequence as given below:

(n2 – 1), (n2 + 1), (n2 – n), (n3 – n), (n2 – n + 1), (n2 – n – 1), etc 

If numbers in the series are 1,5, 11, 19, 29 and so on, then the relation is (n2 – n – 1).

Example: If numbers in the series are 21, 31, 43, then the relation is (n2 – n + 1) 

If n = 5, (52 – 5 + 1) = 21

If n = 6, (62 – 6 + 1) = 31

If n = 7, (72 – 7 + 1) = 43 

So you have to find the number which is out this series.