Final answer:
The probability of randomly picking a blue marble from a bag containing 3 blue, 7 red, and 5 yellow marbles is 1/5, which is option a.
Step-by-step explanation:
The probability of picking one marble of a specific color from a bag depends on the number of that color's marbles compared to the total number of marbles in the bag. In this case, to find the probability that a randomly picked marble will be blue, you would divide the number of blue marbles by the total number of marbles.
Given there are 3 blue marbles and a total of 15 marbles (3 blue + 7 red + 5 yellow = 15), the probability is:
Probability of blue marble = Number of blue marbles / Total number of marbles = 3/15. This simplifies to 1/5, which corresponds with option a. Therefore, the correct answer is 1/5.