Solution
We have
5 red marbles
6 blue marbles
3 green marbles
4 black marbles
2 yellow marbles
For a total of 5+6+3+4+2 = 20 marbles
And we want to find the following probability:
p(green or black) = P(green) + P(black) - P(green and black) = 3/20 + 4/20 - 0/20 = 7/20
Equivalent to : 7/20 * 5/5 = 35/100
p(green and red) without replacement = 0/100