A bag contains 20 balls, 3 are coloured red, 6 are coloured green, 4 are coloured blue, 2 are coloured white and 5 are coloured yellow. One ball is selected at random. Find the probabilities of
the following events
I. The ball is either red or green
II. The ball is not blue
III. The ball is either red or white or blue. (Hint: consider the complementary event.)