Probability Probability is a numerical measure of the likelihood of the event. The probability of an event is the measure of the chance that the event will occur as a result of an experiment. The probability of an event A is the number of ways event A can occur divided by the total number of possible outcomes. The mathematical theory of probability deals with patterns that occur in random events. Directly or indirectly, probability plays a role in all activities. Probability is used in analyzing games of chance, genetics, weather prediction, and a myriad of other everyday events. It helps in predicting random inheritance of genes by offspring from parents; random mutation; the bottom–level mechanism on which evolution by natural selection operates (population genetics). Other major applications of probability theory in everyday life are in risk assessment, in trade on commodity markets and reliability. Many consumer products, such as automobiles and consumer electronics, utilize reliability theory in the design of the product in order to reduce the probability of failure. The probability of failure may be closely associated with the product's warranty.