Probability is a way of assessing chance, likelihood or risk. It may be quoted as a decimal, fraction or percentage. The probability of an impossible event is 0 and the probability of a certain event is 1. All other probabilities are between 0 and 1.

## Software/Applets used on this page

## Glossary

### event

any set of possible outcomes of a statistical experiment

### fraction

A ratio of two numbers or polynomials.

### union

The union of two sets A and B is the set containing all the elements of A and B.