The quadratic mean (or root mean square, or R.M.S.) is usually used in physical applications. In power distribution systems, for example, voltages and currents are usually referred to in terms of their R.M.S. values.
The quadratic mean of a set of scores is obtained by squaring each score, adding the results, dividing by the number of scores n, and then taking the square root of that result. For example, the quadratic mean of 2, 4, and 10 is

Find the R.M.S. of these power supplies (in volts): 151, 162, 0, 81, 268.

A +164-100- /120-v 40 = 6.3 71