A bag contains 28 blue marbles and 12 red marbles. If Milton removes two marbles without replacing them, what is the probability that the first marble will be blue and the second one will be red?

The probability the first marble will be blue is 28/40

The probability the second marble will be red is 12/39

The reason is because 28 + 12 = 40, so this makes the denominator for our first outcome, but then a marble is removed making our denominator 39 because 40-1 = 39.