So if we want to calculate the exact probability of an event occurring
how do we do it in general?
To see how, we will need some notation.
Notation    P(A) is the probability that event A will occur.
     P(A) =                     The number of ways event A can occur              .
                       The total possible number of ways all outcomes can occur
General properties of probability
1) P(A)=1 means event A must occur (100% chance A will occur)
2) P(A)=0 means event A can not occur (0% chance A will occur)
3) Otherwise  0 < P(A) < 1