Descriptive Statistics and Introduction to Probability Practice Test

In statistics, the sum of all observations is written with the summation symbol Σ. It signals you to add every value in the data set, usually shown as x1 + x2 + ... + xn, or compactly ∑_(i=1)^n x_i. This differs from x̄, which is the average (mean) of the observations, μ, the population mean, and N, the total number of observations. So Σ is the symbol used to denote the total sum.