CK-12 Probability and Statistics - Advanced

http://www.ck12.org Chapter 4. Discrete Probability Distribution

P(x)≥0, for all values ofx

∑

x

P(x) = 1

The symbol∑xP(X)means "add the values ofP(x)for all values ofx"

Example:

What is the probability distribution of the number of yes votes for three voters (see the first example in the first
section Introduction)

Solution:

Since each of the 8 outcomes is equally likely, the following table gives the probability of each value of the random
variable.

TABLE4.2:

Value of Random Variable

(number of Yes votes) Probability

Probability

3 1 / 8 = 0. 125

2 3 / 8 = 0. 375

1 3 / 8 = 0. 375

0 1 / 8 = 0. 125

Figure:Tabular Representation of the Probability Distribution for the Random Variable in this Example.

The table and the graph are two ways to show the probability distribution. Note that the graph of a probability
distribution can be either a line graph or a bar graph.