. . Mathematical Expectation Introduction An extremely useful concept in problems involving random variables or distributions is that of expectation. Random variables can be characterized and dealt with effectively for practical purposes by consideration of quantities called their expectation.
The concept of mathematical expectation arose in connection with games of chance. For example, a gambler might be interested in his average winnings at a game, a businessman in his average profits on a product, and so on. The average value of a random phenomenon is also termed as its Mathematical expectation or expected value. In the following sections, we will define and study the concept of mathematical expectation for both discrete and continuous random variables, which will be used in the following subsection.
. . Expected value and Variance Expected value The expected value is a weighted average of the values of a random variable may assume. The weights are the probabilities.
Definition . Let X be a discrete random variable with probability mass function (p.m.f.) p x ( ) . Then, its expected value is defined by E X x p x