• The expectation (expected value) of a discrete random variable is the mean of its probability distribution.
• It represents the average of the values we obtain in the long run when the experiment is repeated many times.
• It is denoted by μ or E(X), and it is calculated by:

μ = Σ (x × f(x))

• That is, we multiply each value by its probability and add the products.
• The expectation does not have to be one of the possible values of the variable.
• For example, when a fair die is rolled, the expectation is 3.5, which cannot appear in a single roll.