Jeff has 8 red marbles, 6 blue marbles, and 4 green marbles that are the same size and shape. He puts the marbles into a bag, mixes the marbles, and randomly picks one marble. What is the probability that the marble will be blue?

The total number of marbles in the bag is 8 (red) + 6 (blue) + 4 (green) = 18 marbles.

The probability of picking a blue marble is 6 (number of blue marbles) / 18 (total number of marbles) = 6/18 = 1/3.

Therefore, the probability that the marble picked will be blue is 1/3.