Introduction to the probability of an event

Probability is the likelihood or chance that a certain event will occur in an experiment.

An experiment can be as simple as spinning a spinner or picking a marble from a bag.

An outcome is a result of an experiment. For example, if cards are labeled 1 – 10, there are 10 outcomes; a 1 is picked, a 2 is picked, . . ., a 10 is picked. 

An event is a collection of outcomes. An event can consist of none of these outcomes, one of these outcomes, through all 10 of these outcomes. For example, an event can be that an even number was chosen.

For experiments with equally likely outcomes, the following formula is used to find the probability of an event. 


Probability of an impossible event = 0 (or 0%)

Probability of a certain event = 1 (or 100%)