A bag contains five white balls and eight black balls. Your goal is to draw two black balls.
a) You simultaneously draw two balls at random. What is the probability that they are both black?
b) You simultaneously draw two balls at random. Once you have drawn two balls , you put back any white balls , and redraw so that you again have two drawn balls What is the probability that you now have two black balls ? (Include the probability that you choose two black balls on the first draw.)