A random variable is a variable that takes different real values as a result of the outcomes of a random event or experiment. To put it differently, it is a real valued function defined over the elements of a sample space. There can be more than one random variable associated with an experiment. For example, if a coin is tossed ten times, one random variable associated with this experiment could be the number times the head shows up, a second random variable could be the number times the tail shows up and a third random variable could be the difference between number of times the head shows up and the number of times the tail shows up. We can define many more random variables associated with this experiment.