This is a fairly easy tutorial that can be done in just a few minutes.
The first thing that needs to be done is to create a new symbol. For my tutorial I called it "Number". Now edit "Number" and put a 0 in the center with a light grey color. Create a new keyframe on the second frame, then make the 0 a slightly darker color.
Now create one more key frame at frame 5.
Go back to the first frame and create an action with these properties:
Set Variable: "index" = 0
Set Variable: "loop" = Int (Random (10))
Now go to the fifth frame and create an action with these properties:
If (index<=loop)
Set Variable: "index" = index+1
Go to and Play (2)
End If