Example

The probability of

getting two heads or two tails

in an experiment involving a sequence of

two flips of a fair coin

is the value

\[\begin{equation*}
  \Pr(A) = \frac{|A|}{|\Omega|} = \frac{2}{4} = \frac{1}{2},
\end{equation*}
\]

with the event and the sample space

\[\begin{align*}
  \Omega & = \{
  (\mathrm{H}, \mathrm{H}),
  (\mathrm{H}, \mathrm{T}),
  (\mathrm{T}, \mathrm{H}),
  (\mathrm{T}, \mathrm{T})
  \}
  \\
  A & = \{
  (\mathrm{H}, \mathrm{H}),
  (\mathrm{T}, \mathrm{T})
  \},
\end{align*}
\]

respectively,