What is the probability of picking a green marble, then a green marble if you do not put back the first marble?

The correct answer is 3/95.
The probability of picking a green ball marble at first is 4/20 (total number of green marbles/ total number of marbles present).
Since the first green marble is not returned, the probability of picking another green marble 3/19
Multiply both results
4/20 * 3/19
= 12/380
= 3/95.