We will have the following:
All the outcomes for the event of choosing a letter from A to D are:
[tex]\frac{4}{8}=0.5[/tex]So half the times a ball is picked there should be one from letter A to D.
***Explanation***
We have the following set:
[tex]\mleft\lbrace A,B,C,D,E,F,G,H\mright\rbrace[/tex]So, the set has a magnitude of 8 [Since it has 8 components].
When we pick any given value from the set we will have that we will have to pick 1 value from the total set, that is:
[tex]\frac{1}{8}[/tex]But, when we are asked of the event of taking specific values from to D we are asked to pick 4 specific values:
[tex]\mleft\lbrace A,B,C,D\mright\rbrace[/tex]That set has a magnitude of 4. So, in order to determine the event of picking a value from the second set on the first set, we will have:
[tex]p=\frac{4}{8}\Rightarrow p=\frac{1}{2}\Rightarrow p=0.5[/tex]This event is represented by "p" the probability of that happening. So, the probability of the event happening [Selecting one of the balls of the specific set] is 1/2; in other words, each time you pick there is a 50% chance you will get one of the values of the smaller set.