Answer:
1/19
Step-by-step explanation:
11 blue marbles, 4 green marbles, and 5 purple marbles = 20 marbles
P( green) = green / total = 4/20 = 1/5
Now keep the green
11 blue marbles, 3 green marbles, and 5 purple marbles = 19 marbles
P(purple) = purple/ total = 5/19
P(green, keep,purple) = 1/5 * 5/19 = 1/19