SSC Reasoning preparation tips: Series Completion

Series completion is a very important and trickier topic of both verbal and non-verbal reasoning. There are numerous questions out of this section, which is not only asked in SSC exams but also in other competitive exams. There are nearly 1-2 questions are asked from Series verbal reasoning in SSC Tier-1 exams and same number of questions are asked from series non-verbal reasoning.

In series completion questions, a series of numbers, alphabets and both are given. These terms follow a certain pattern throughout. The aspirants need to recognize this implicit pattern and use it to complete the series or find the wrong element in the series. Now, you may be thinking that how to recognize the hidden pattern.

In this article, we are sharing the tricks to recognize the hidden pattern in the series with some most frequent patterns found in the series questions. Let us take a tour of it.

How to prepare for Series completion in Reasoning?

The pattern, which you have to recognize can be of various kinds. Once you have identified it, then you can apply it to the other numbers to find out the missing or wrong number in the series. Check below the list of these common patterns, which are most frequently asked in SSC exams.

Prime numbers

When numbers in series are prime numbers, which are divisible by own and greater than 1. There must not be any factor of this number. Such numbers are- 11, 13, 17, 19, etc.


When numbers in the series are of perfect square or perfect cube or perfect square roots or cube root. Such numbers include 81, 100, 121, 144, etc. These can be of decimal nature.

Pattern in differences

Calculate the differences between the numbers given in the series provided in the question. This difference can be constant or varying in nature. After identifying this difference, you can find the problem number or words or letters in the problem series.

Example:- 2, 7, 12, 17, 22, ?

The difference in this series for every number is 5. Hence, the next number will be 27.

Example:-  A, D, G, J, ?

The difference between the position of these letters is 3. So, The next third letter to J will be M.

Pattern in Alternate numbers

Whenever there is a pattern in the alternate numbers or letters or words in the series, then with this alternate pattern, you can easily find the problem number, letter or word.

Example:- 2, 3, 4, 7, 6, 11, ?

In this series, the alternate numbers are incremented by 2 and 4 successively. Hence, the next number will be 8.

Similar can be done to letter series or word series to find the answer.

Geometric Series

When numbers in the series follow the geometric progression means when each successive number in the series is obtained by multiplying or dividing the previous numbers with a fixed ratio, then problem number  can be easily figured out.

Example: 4, 20, 100, 500, ?

Each number is multiplied by 5 and in geometric progression. Hence, the next number will be 2500.

Pattern in the adjacent numbers

When adjacent numbers are varying with a logical pattern in the series, it can be understood with the following example.

Example: 2, 4, 12, 48,?

In this series, first number is multiplied by 2, second number is multiplied with 3 and third one is with 4. Hence, the next number in series will be 240.

Odd one out

All numbers but one is in the series. Such numbers can be identified for elimination.

Complex Series

In such series, the differences between numbers are dynamic instead of being fixed, but still there is a clear logical rule.

Example: 3, 8, 15, 24, 33, ?

In this series, numbers are incremented by +5, +7, +9 and +11. Hence, the next number will be increment by +13. So, the solution will be 46.

Complex arithmetic functions

In some series, more than one operation (+, x, – and /) is used successively. Such pattern are very tough to recognize and sometime take a lot of time. So, it is advisable not to spend so much time on such questions. If you find the correct answer under the expected time limits, then only attempt it otherwise switch to the next question.

Example: 4, 6, 12, 14, 28, ?

In this series, each prospective number is incremented by 2 and the next number is multiplied by 2. Hence, applying this logic to the series, the next number will be 30.

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