## About Probability

## Opening

# About Probability

Discuss the following with your classmates.

In everyday life, people often think about whether or not something might happen in the future. Many decisions are based on the chance or probability that a particular event may or may not occur.

Probability involves the study of events whose results are affected by chance. The probability of an event is expressed as a ratio that can be used to predict the likelihood of an event occurring. Probability ratios are values ranging from 0 to 1. Probability ratios may be represented as fractions, decimals, or percentages. If an event has a probability equal to 0, then it is impossible. If an event has a probability equal to 1, then it is certain.

The theoretical probability of a particular event *A* is the ratio of the number of ways that* A* can occur to the number of all possible outcomes.

This is represented by the probability formula:

*P*(*A*) = $\frac{a}{n}$

where

*a*is the number of ways that an event can occur*n*is the total possible outcomes

Probability is a number between 0 and 1 used to quantify likelihood for processes that have uncertain outcomes (such as tossing a coin, selecting a person at random from a group of people, or tossing a ball at a target).