Answer
$\dfrac{11}{20}\text{ or } 0.55$
Work Step by Step
Use the formula for a probability $P$ as: $\text{Probability}=\dfrac{\text{Number of favourable outcomes}}{\text{Total number of possible outcomes}}=\dfrac{n(E)}{n(S)}$
Here we have:
Number of green balls =$8$;
Number of orange balls = $3$.
Not white in this case means green or orange.
Hence, there $8+3=11$ non-white balls so $n(E)=11$.
There are $20$ balls in total, so $n(S)=20$
Thus, the probability is:
$P\left(\text{selecting a ball non-white ball}\right)=\dfrac{11}{20}=0.55$.
