# Probability mass function

### From Conservapedia

In probability theory, a **probability mass function** (*p(x)*) is a real-valued function of a discrete variable (*x*), such that the value *p(x _{k})* is the probability of the variable

*x*having the value x

_{k}.

In order to qualify, such a function must meet the following criteria:

∑ *p*(*x*_{k}) = 1*k*

The collection of pairs ( x_{k} , p(x_{k}) ) is the discrete probability distribution of *x*.