Probability is a measure of how likely an event will occur. Mathematically, it is expressed as the ratio of the number of occurrences of the event to the number of all possible outcomes.
For example, the probability of getting a 3 when rolling a die is 1/6, since there are 6 possible outcomes (i.e 1,2,3,4,5 or 6) and only one of them is 3. The probability of getting an even number therefore is 3/6 = 1/2 since there are 3 possible outcomes which are even number (2,4,6).
The formula for probability of event is defined as follows:
The value of the probability of an event range from 0 to 1 (i.e. ). Probability value of 0 means the event is impossible and the probability value of 1 means the event is sure to happen.
Probability theory is applied in many fields such as finance, statistics, gambling, science, etc.