Answer
$\dfrac{3}{10}$ or, $30 \%$
Work Step by Step
The probability that the point is on $\overline{MN}$ is equal to the ratio of the length of $\overline{MN}$ to the length of $\overline{ZB}$.
$\text{P(point on $\overline{MN})$}=\dfrac{MN}{ZB}$
Therefore,
$\text{P(point on $\overline{MN})$}=\dfrac{20-5-9}{20}=\dfrac{3}{10}$ or, $30 \%$
