Description: In order to find the probability of picking a yellow marble from a bag, we have to first determine the number of possible outcomes, and then how many of them meet our constraints. Created by Sal Khan and Monterey Institute for Technology and Education. Find the probability of pulling a yellow marble from a bag with 3 yellow, 2 red, 2 green, and 1 blue marbles. And so this is sometimes the event in question, right over here, is picking the yellow marble. I'll even write down the word "picking."*Teacher Advisor is 100% free.