Cherise has a bag of marbles for her little sister. it contains 10 orange marbles, 7 yellow marbles, and 3 green marbles. she drops the bag and 3 marbles roll out. what is the probability that all 3 marbles are yellow?

The probability of the first marble to be yellow is: 7/20
(where u is the number of yellow marbles and 20 is the total number of marbles)

The probability of the second marble to be yellow is: 6/19

The probability of the third marble to be yellow is: 5/18

The probability that all 3 marbles are yellow:
7/20 * 6/19 * 5/18 = 210/6840 = 0.03 = 3%

Hope that helps you