A bag contains 4 marbles, 6 green marbles, and 2 red. you select one ball by random. What is P red?

p (outcome) = (number of desired outcomes) / (total number of outcomes)

The total number of outcomes is the sum of the numbers of the marbles.

4 + 6 + 2 = 12

The desired outcome is selecting a red ball. There are 2 red balls, so the number of desired outcomes is 2.

p (red) = 2/12 = 1/6