An average is a number that shows a middle or normal value for a set of data. It is calculated by adding all the data points then dividing the total by the number of data points. A running average is an average that continually changes as more data points are collected. Calculating a running average requires repeated calculations.

### The Average

Imagine that you want to know the average number of people who attend your community's monthly town hall meetings this year. Suppose there have been four meetings so far and the data set shows how many people have attended each meeting, for example:

{24, 30, 27, 18}

To calculate the average attendance, add the numbers and divide the sum by four:

Average = (24 + 30 + 27 + 18) / 4 = 99 / 4 = 24.75

### The Running Average

The average number of people who have attended each town hall meeting is 24.75. But that number is likely to change next month when a new town hall meeting is held. This is when you begin calculating the running average. Add the next meeting's number of people to the previous month's total and divide by the new number of meetings. If 35 people attended the next meeting, the calculation would be:

Running average = (99 + 35) / 5 = 134 / 5 = 26.8

### Follow-up Meetings

The running average will continue to change as more meetings take place. If 41 people attended the sixth meeting, the calculation would be:

Running average = (134 + 41) / 6 = 29.2