• The probability distribution of a discrete random variable X is a listing of each possible value x taken by X along with the probability P(x) that X takes that value in one trial of the experiment. 
  • The mean \mu of a discrete random variable X is a number that indicates the average value of X over numerous trials of the experiment. It is computed using the formula \mu=\Sigma x P(x). 
  • The variance \sigma^{2} and standard deviation \sigma of a discrete random variable X are numbers that indicate the variability of X over numerous trials of the experiment. They may be computed using the formula \sigma^{2}=\left[\Sigma x^{2} P(x)\right]-\mu^{2}, taking the square root to obtain \sigma.