Definition For both Discrete random variable and Continuous random variable F(x)=P(X≤x) for −∞<x<∞ F is non-decreasing function limx→∞F(x)=1 limx→−∞F(x)=0 F is right continuous. That is, for any b and any decreasing sequence bn,n≥1, that is converges to b limx→∞F(bn)=b