Q. What is xi in mean formula?

In the mean formula, xix_ixi represents an individual observation or data value. Each xix_ixi is one element of the dataset being averaged.

Using indexed values like x1,x2,x3x_1, x_2, x_3x1,x2,x3 helps organize data systematically, especially in large datasets. This notation is standard in statistics, research, and data science.