30 points? Answer and explanation​

Answer:
[tex]\large\boxed{\dfrac{4}{5}=0.8}[/tex]
Step-by-step explanation:
We have:
10 - number of all marbles
4 + 3 + 1 = 8 - number of non-white marbles
The probability:
[tex]\dfrac{non-white}{all}=\dfrac{8}{10}=\dfrac{8:2}{10:2}=\dfrac{4}{5}[/tex]