Answer
$\dfrac{3}{5} \text{ or } 0.6$
Work Step by Step
Use the formula for a probability $P$ as: $\text{Probability}=\dfrac{\text{Number of favourable outcomes}}{\text{Total number of possible outcomes}}=\dfrac{n(E)}{n(S)}$
Not green in this case means it is white or orange.
Here we have:
Number of white balls = $9$;
Number of orange balls = $3$.
Number of green balls = $8$.
There are $9+3=12$ non-green balls so $n(E)=12$ .
There are $20$ balls in total, so $n(S)=20$
Thus, the probability is:
$P\left(\text{selecting a non-green ball}\right)=\dfrac{12}{20}=\dfrac{3}{5}=0.6$.
