# Number and Alphabet series

## What is Series?

It is a sequential order of letter, numbers or both arranged in a particular pattern, i.e. there is some specific underlying rule which dictates which terms will come in that series.

These rules may vary a lot - they may be based on mathematical logic, or the nature of the elements of the series or alphabetic positions of letters etc. This is what we need to do in questions of series - decipher the underlying rule. That is , we are supposed to reverse engineer.

If one of the following is true, then the series question can be called as wrong:

- There is no one consistent pattern/rule that can justify all the terms in that series.
- If you can find 2 or more patterns/rules, which lead to different answers and both of those answers are present in the answer options.

However, the question cannot be called wrong in the following cases:

- There is only one pattern/rule, that leads to a single answer.
- If you can find 2 or more patterns/rules, which lead to different answers, but only one of those answers is present in the answer options.
- If you can find 2 or more patterns/rules, which lead to the same answer.

## Types of Series Questions

In series, be it alphabetic or numeric series, you will find two major type of questions:

Find the missing term - the missing term may be at the end or somewhere in the middle of the series.

Find the incorrect term - one of the term in the series will be incorrect and you will have to identify that incorrect term that does not follow the general pattern/rule of the series. These questions are often a little more challenging than the missing term questions.

The series may be of one of the following types:

- Number Series
- Letter Series
- Alpha – Numeric Series
- Continuous Pattern Series
- Diagram based number and letter series

Let’s study all these different types of series in succeeding sub-modules.