A = {1, 2, 3}, B = {x, y, z}

A × B = {(1, x), (1, y), (2, x), (2, y), (3, x), (3, y)} Suppose the possible outcomes of a random process are real numbers a₁, a₂, a₃,..., a(n), which occur with the probabilities p₁, p₂, p₃,..., p(n). The expected value of the process is,

∑a(k)p(k) = a₁p₁ + a₂p₂ + a₃p₃ +...+ a(n)p(n) for 1 ≤ k ≤ n ;