Answer
$\begin{array}{cc}
&\bf{\text{Outcome}} &\bf{\text{Probability}}
\\&HH &0.25
\\&HT &0.25
\\&TH &0.25
\\&TT &0.25\end{array}
$
Note: HH means the outcome is head-head
Work Step by Step
Let
H = the outcome of a toss is a head
T = the outcomes of a toss is a tail
In tossing two fair coins once, the possible outcomes are: HH, HT, TH, TT.
Thus, the sample space is: $S=\left\{HH, HT, TH, TT\right\}$
Since the coin is fair, the outcomes of the sample space are equally likely to occur.
Thus, each outcome has a probability of $0.25$ or $\frac{1}{4}$.
Therefore, the probability model is:
$\begin{array}{cc}
&\bf{\text{Outcome}} &\bf{\text{Probability}}
\\&HH &0.25
\\&HT &0.25
\\&TH &0.25
\\&TT &0.25\end{array}
$
Note: HH means the outcome is head-head
