This section talks about the concept of central tendency, mean and median [during even and the odd number of observations] with examples. It introduces the concept of measure of dispersion. In this chapter, we shall learn some of the important measures of dispersion and their methods of calculation for ungrouped and grouped data. The topics that students learn in the chapter include measures of dispersion, range, mean deviation, variance and standard deviation of ungrouped/grouped data and analysis of frequency distributions with equal means but different variances.