Answer
$\dfrac{11}{20}$ or $0.55$
Work Step by Step
We know that $\text{probability}=\frac{\text{number of favourable outcomes}}{\text{number of all outcomes}}=\frac{n(E)}{n(S)}.$
The balls is not white means it is green or orange.
Hence, we have
$8+3=11$ green or orange balls, so $n(E)=11$
There are a total of \div$20$ balls so $n(S)=20$
Therefore,
$P\left(\text{selected ball is not white}\right)=\dfrac{11}{20}=0.55$
