# 6: Expected Value and Variance

- Page ID
- 3143

- 6.1: Expected Value of Discrete Random Variables
- When a large collection of numbers is assembled, as in a census, we are usually interested not in the individual numbers, but rather in certain descriptive quantities such as the average or the median.

- 6.2: Variance of Discrete Random Variables
- The usefulness of the expected value as a prediction for the outcome of an experiment is increased when the outcome is not likely to deviate too much from the expected value. In this section we shall introduce a measure of this deviation, called the variance.