A random variable is a number that represents an outcome from a random experiment or circumstance. A random variable can be discrete or continuous. A discrete random variable can have only countable distinct values, such as 0, 1, 2, 3, …. Examples include the number of students in a classroom, the number of airplanes at the airport, or the number of defects in a lot. A continuous random variable can have any value, such as from a measurement. Examples include the height of subjects in your study, the weight of cereal boxes, or the length of screw drivers.