Random variables

Math

Definition

A variable whose value is determined by the outcome of a random process. Discrete random variables take countable values (like number of heads), while continuous random variables take any value in an interval (like height).

Examples

  • X = number of heads when flipping a coin 10 times (discrete)
  • X = the exact time a bus arrives (continuous)
  • X = the sum of two rolled dice (discrete, values 2-12)
Key Fact

E(X) = Σ[x · P(x)] for discrete; Var(X) = E(X²) - [E(X)]²

Related Terms

Binomial distribution Normal distribution Standard deviation Basic probability

Study This Concept

Practice random variables with free review games in these units:

AP Statistics Unit 4: Probability Random Variables and Distributions