Consider rolling a die thirty times. In each trial, the outcome can be anything from one to six. If one comes up six out of thirty times, its probability is six over thirty, and so on. Each of these outcomes, known as random variables, has a single numerical value determined by chance. It represents all the possible outcomes of an experiment. The lower case letter x denotes the numerical value of the random variable. Random variables can be discrete or continuous. Discrete random variables can be associated with a counting process, either finite or infinite. For example, a hen may lay one egg, two eggs, or more, but not 1.27 eggs. Conversely, continuous random variables have infinitely many values that can be associated with measurements without gaps or interruptions on a continuous scale. For example, in a day, a cow may produce anywhere between zero to twenty liters of milk, measured on a continuous scale.