Suppose X is a discrete random variable with range \(R = {x_1, x_2, ..., x_n}\text{.}\) The arithmetic mean is given by

If this data comes from sample data then we call it a sample mean and denote this value by \(\overline{x}\text{.}\) If this data comes from the entire universe of possibilities then we call it a population mean and denote this value by \(\mu\text{.}\) When presented with raw data, it might be good to generally presume that data comes from a sample and utilize \(\overline{x}\text{.}\)