OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO
I have a bag of three balls. One of them is green and the others are either red or green. If I select one ball at random, what is the chance that it will be red?
OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO
I will assume you're not color blind.
Calculate the probability that your bag looks like each of the following:
O O O
O O O
O O O
Then calculate the probability of getting a O from each of those bags.
For each bag calculate (probability of bag)(probability of O from that bag). Add the results.