A bag contains r red and b blue balls. You reach into the bag and take k balls. Let R be the number of red balls you take. Let B be the number of blue balls. Express the following events in terms of the random variables R and B:
(a) You pick no red balls.
(b) You pick one red and two blue balls.
(c) You pick four balls.
(d) You pick twice as many red balls as blue balls.