Amount of balls = 9.
Q1)
a) Pick a yellow ball (3/9), replace, then pick a black ball (2/9). Probability is 3/9 * 2/9 = 2/27.
OR pick a black ball first (2/9), replace, then pick a yellow ball (3/9). Probability is 2/27.
Add both to get 4/27.
b) Yellow first (3/9), do not...