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8.2 VARIANCE and STANDARD DEVIATION:, , The main drawback of the range is that it is, based on only two values, and does not consider, all the observations. The variance and standard, deviation overcome this drawback as they are based, on the deviations taken from the mean., , 8.2.1 Variance:, , The variance of a variable X is defined as the, arithmetic mean of the squares of all deviations of, X taken from its arithmetic mean., , It is denoted by Var(X) or o? ., , Var (X) = 6? = “5 (- ¥P