Method: Make mathematical hypotheses to determine probability of an event.
The four properties of probability:
1. Event occurs.
P (x occurs) + P (x does not occur) =
2. Occurrence at different times; when
x and y occur at different times.
P (either x or y occurs) = P(x occurs)
+ P(y occurs)
3. X and y are independent. Y is not
more likely to happen when A happens than when A does not happen.
P(x and y both occur) = P (x occurs)
* P (y occurs)
4. Other influxes. When x occurs, y has
to occur, too.
P (x occurs) <= P (y occurs)