A discrete probability distribution is a
function with a domain whose elements are the discrete values
that a discrete random variable can assume, and a range whose
elements are the probabilities associated with the values in the
domain. The domain of a discrete probability distribution
consists of the sample points of a discrete sample space. The sum
of all the probability values in the range is equal to 1. The
mean and variance of a discrete probability distribution are the
mean and variance, respectively, of all elements in its range.