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,
where | \(\mathrm{H}\) | is a symbol denoting “heads” |
\(\mathrm{T}\) | is a symbol denoting “tails”. |