This section first defines discrete and continuous random variables. Then, it introduces the distributions for discrete random variables. It also talks about the mean and variance calculations.
is a listing of each possible value 
taken by along with the probability 
that takes that value in one trial of the experiment. 
of a discrete random variable is a number that indicates the average value of over numerous trials of the experiment. It is computed using the formula 
. 
and standard deviation 
of a discrete random variable are numbers that indicate the variability of over numerous trials of the experiment. They may be computed using the formula ![\sigma^{2}=\left[\Sigma x^{2} P(x)\right]-\mu^{2}](https://dev.saylor.org/filter/tex/pix.php/8070f4b80ee1dcc04ecf7c91b61a09a7.svg "\sigma^{2}=\left[\Sigma x^{2} P(x)\right]-\mu^{2}")
, taking the square root to obtain .