I: A box contain 20 screws, 5 of which are defective, 2 screws are drawn at random.The probability of event that neither of the two screws is defective is 21/38.
II: A box contains 5 black, 4 white and 6 red balls. 2 balls are drawn without replacement. The probability that the first will be white and the second will be black is 4/21