In this Introduction to Probability, we're going to be pretty general and not-at-all technical.

In a nutshell:

Probability is a number from $0$ to $1$.
A value of $0$ indicates that something will never happen.
A value of $1$ indicates that it is guaranteed to happen.
Probability can be presented as a decimal, a fraction, or a percentage:
- $0.25 = \frac{1}{4} = 25\%$
To calculate the probability of an event occurring, create a fraction that has in the numerator the number of cases that make you happy and in the denominator the total number of cases (see below).

$probability$ $=\frac{number \ of \ cases \ that \ make \ me \ happy}{total \ number \ of \ cases}$

Example

When rolling a fair, $6$-sided die, what is the probability of rolling a number that is a multiple of $3$?

Number of cases that make us happy

Two: $3$ and $6$

Total Number of Cases

Six: $1, 2, 3, 4, 5, 6$

probability $= \frac{2}{6} = \frac{1}{3}$