Balls are randomly removed from an urn that initially contains 20 red and 10 blue balls. What is the probability that all of the red balls are removed before all of the blue ones have been removed?

Balls are randomly removed from an urn that initially contains 20 red and 10 blue balls.
(a) What is the probability that all of the red balls
are removed before all of the blue ones have
been removed?
Now suppose that the urn initially contains 20
red, 10 blue, and 8 green balls.
(b) Now what is the probability that all of the red
balls are removed before all of the blue ones
have been removed?