When we do something we call it an experiment and the outcomes of that event are taken as separate events. For example: throwing a dice is an experiment and getting a multiple of 2 as outcome is one of the possible events. The ratio of total number of favorable outcomes to an event to the total number of outcomes possible in that experiment is known is probability of that event. In simple words probability is just the possible chances of occurrence of an event. Probability always lies between 0 and 1. When probability is equal to zero, then the event is said to be an impossible event. When the probability is equal to one, we call the event a sure event.