An *event* is something that can be either true or false

ex. You may win the lottery next year

The *probability* of that event is a rational evaluation of
how much we believe the event is true, given *all* the
information available to us

Often we see the definition \[\text{Probability}=\frac{\text{positive cases}}{\text{total cases}}\]

The problem is **how do we count positive and
total cases?**

Example: We have several red and blue cards, and we take one randomly.

What is the probability that the card is blue?

If we know all possible

*outcomes*, and they are “symmetric”, then each one of them has the same probability- For instance, all the dice sides are “symmetric”, thus they have all the same probabilities

If the event is true only for a set of outcomes, and the outcomes are “symmetric”