Discrete Distributions
It is said that a random variable X has a discrete distribution or that X is a discrete random variable if X can take only a finite number k of different valuesx_1,…,x_k or, at most, an infinite sequence of different valuesx_1,x_2,… Random variables that can take every value in an interval are called continuous and are discussed in Section 3.2. If a random variable X has a discrete discrete distribution, the probability function (abbreviated p.f) of X is defined as the function f such that for every real number x,
f(x)=Pr(X=x).