Probability Distributions  
Summary 
a random variable is a variable whose value, which cannot be known beforehand, is determined by the outcome of an experiment. the probability of its occurrence can be predicted. discrete random variables are often the result of a counting process and are often whole numbers. continuous random variables are often the result of measurement and are usually from the set of real numbers. a probability distribution or probability function is a table which shows the probabilities associated with each value of a random variable. the sum of the probabilities in the probability distribution of a discrete random variable always add up to 1. a probability function can also be written as a formula where each value of x is substituted into the formula to give the probablity that the value x will occur. 
key skills 

Vocabulary 
discrete random variable, continuous random variable, probability function, probability distribution, probability, random variable 