After completion of this chapter, students will be able to:

- find the mean, median and quartile of non- grouped data.
- find the mean, median and quartile of grouped data.

The arithmetic mean is defined as the total sum of observations divided by the total number of observations. Here we study about the arithmetic mean of continuous series. Calculation of arithmetic means in continuous series When the number of items is large, we have to divide them into groups. Such groups are known as simple classes. It should be noted that there is no gap between any two successive intervals. So the data is continuous and the series is called continuous series.

The median is defined as the positional value in the set of data arranged in order. The median divides the total number of observations into two equal parts. Therefore, there are 50% items more than the median value.

If three numbers divide the series into four equal parts then, these three numbers are called quartiles.