... it natural to use the mean and the standard deviation together.In the case of a symmetric random variable, the median and the mean agree.However, the interquartile range and the standard deviation ... for the left hand and, foreach such choice, there are three ways to choose a ring for the right hand.Hence, there are 4 ·3 = 12 ways to choose a ring for each hand. This is an instance of a general ... introduced one important measure of centrality, the expected valueof a random variable (the population mean, µ), and one important measureof dispersion, the standard deviation of a random variable...