A jar contains 5 red marbles, numbered 1 to 5, and 12 blue marbles numbered 1 to 12.
a) A marble is chosen at random. If you're told the marble is red, what is the probability that it has the number 3 on it?
b) The first marble is replaced, and another marble is chosen at random. If you're told the marble has the number 1 on it, what is the probability the marble is red?