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”.