Karen wants to distract her noisy four-year-old child at a restaurant. She pulls out a bag that has 4 black marbles, 8 red marbles, and 9 green marbles. The child likes green marbles. What is the probability Karen will randomly pick a green marble from the bag in one try?

Question

kirbykirby · Answer

In total, there are 4 + 8 + 9 = 21 marbles 
The probability getting green in the first try then is:
$$ P(green) = \frac{\text{# green marbles}}{\text{# all marbles}}$$

anonymous · Answer

3/7