Probability

Probability

If the sample space consists of N outcomes and the probabilities p of the elementary events are all equal, then

p = 1 / N

An event A consisting of r elements then has a probability

$\begin{displaymath}p({\bf A}) = { r / N }\end{displaymath}$

For the previous example, we get

$\begin{displaymath}p( \text{\{tail\}} ) = { 1/2}\end{displaymath}$

$\begin{displaymath}p( \text{\{head, tail\}} ) = { 2/2}=1\end{displaymath}$

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