Discrete Random Variables
Definition of Random Variable
There are many types of variables in mathematics. Some, called deterministic variables, have a predictible value given by a rule or relation. But in other cases, variables can depend on chance events. For example:
- the number of players in a football teem that will score a goal in the next match,
- the time it will take you to travel to school tomorrow,
- the sum of the values when three dice are rolled.
This is a throwing dice simulator. n represents a given thrown of the dice, and X is a variable that takes the value of the dice in each thrown.
In this applet, you can simulate up to 1000 throws of a dice. Move the slider n to get a new result, or press the play button to throw it fast.
X is a random variable, as its value depends on a chance event. We can't predict its actual value each time, but we know it is going to be an integer number between 1 and 6.
X is not only a random variable, but a discrete random variable.
Discrete random variables
A discrete random variable X has a set of distinct possible values.
For example, X could be:
- the numbers from the faces of a dice, so X could take the values 1, 2, ..., 6
- the number of defective light bulbs in a purchase order of 50, so X could take the values 0, 1, 2,... , 50
- the number of e-mails a person gets a day, so X could take the values 0, 1, 2,... up to infinity. In this course we will not consider variables like this.