If you select one marble at random from the bag containing 4 blue marbles, 5 red marbles, 1 green marble, and 2 black marbles, we can calculate the probabilities of selecting each color marble.
Total number of marbles in the bag = 4 (blue) + 5 (red) + 1 (green) + 2 (black) = 12 marbles
Probability of selecting a blue marble = Number of blue marbles / Total number of marbles = 4 / 12 = 1/3
Probability of selecting a red marble = Number of red marbles / Total number of marbles = 5 / 12
Probability of selecting a green marble = Number of green marbles / Total number of marbles = 1 / 12
Probability of selecting a black marble = Number of black marbles / Total number of marbles = 2 / 12 = 1 / 6