Probability describes the chance that an uncertain event will occur.

Empirical Probability is an estimate that an event will happen based on how often the event occurs after collecting data or running an experiment ( in a large number of trials). 

               P (head on a coin)  =  1/2
               P (roll a three on a die)  =  1/6

     Biased:  one result has a better chance of happening than
                      another result.

     Unbiased (fair) :  each result has an equal chance of
                      happening. 

Theoretical Probability of an event is the number of ways that the event can occur, divided by the total number of outcomes.
   

       Event:  a set of outcomes. 
          Outcome:  is the result of an experiment or activity.
          Sample Space:  is the set of all possible outcomes.

Example:   Find the probability of tossing a fair die and
                          getting an odd number.

Things to Remember:

The probability of an impossible event is 0. 

The probability that an event is certain to occur is  1.

** The probability of an event cannot be larger than  1.