Answer
$\dfrac{2}{5}$
or, $40 \%$
Work Step by Step
The probability that the light is red is the ratio of the length corresponding to a red light to the total area:
$P(\text{Red Light})=\dfrac{75-45}{75-0}\\=\dfrac{30}{75}\\=\dfrac{2}{5}$
or, $40 \%$
