Answer
The fraction of outcomes which is not less than 5 is $\frac{1}{3}$.
Work Step by Step
We know that the sample space of equally likely outcomes is $ S=\left\{ 1,2,3,4,5,6 \right\}$.
There are six outcomes in the sample space, so $ n\left( S \right)=6$.
And the event of getting a number not less than 5 can be represented by $ E=\left\{ 5,6 \right\}$.
There are four outcomes in this event, so $ n\left( E \right)=2$.
Therefore, the probability of rolling a number not less than 5 is:
$\begin{align}
& P\left( E \right)=\frac{n\left( E \right)}{n\left( S \right)} \\
& =\frac{2}{6}
\end{align}$
Thus, the fraction of outcomes which is not less than 5 is $\frac{1}{3}$.