Number Series is one of the more important topics for IBPS PO. Quite a few questions come from this topic every year. In these questions, a series of numbers along with a missing number is given and the student is asked to find out the missing number.

For a given question, examine the difference between adjacent numbers. A number of times, the difference between adjacent numbers in a series is constant.

Examine if there is a multiplication pattern between the numbers. For example, in the series: 1, 2, 4, 8, 16, … each number is twice the previous number.

If the numbers do not follow an addition or multiplication pattern, check if you can use a rule that involves two or more basic arithmetic functions ( +, -, x, / ). For example, in the series 2, 4, 8, 6, 3,… the rule is: add 2 to the first number to get the second number, then multiply the second number by 2 to get the third number, subtract 2 from the third number to get the fourth number and divide the fourth number by 2 to get the fifth number.

Identifying the wrong number in a series

Sometimes questions are asked on identifying the wrong number in a series. This is more difficult than finding the missing number because in this case, the wrong number might mislead the thought process. One way of solving this is by assuming one of the numbers to be wrong and trying to find the logic connecting the other numbers. If a proper logic is not found, then consider another number to be wrong and repeat the process.

In some questions, two series are given, with the first series being complete and the second series being incomplete. In these questions, the student has to identify the logic that the numbers of the first series follow and apply the same logic to the numbers of the second series. These questions are slightly easier compared to the other two types of questions.