Answer
$\dfrac{3}{5}$ or $0.6$
Work Step by Step
We know that $\text{probability}=\frac{\text{number of favourable outcomes}}{\text{number of all outcomes}}=\frac{n(E)}{n(S)}.$
Here we have:
$9+3=12$ white or orange balls so $n(E)=12$
There are $20$ balls in all so $n(S)=20$
Therefore,
$P\left(\text{selecting a white or orange ball}\right)=\dfrac{12}{20}=\dfrac{3}{5}=0.6$
