Here Is the Answer:
Not replacing the first marble makes the events dependent because the outcome of the first draw affects the probability of the second draw. After the first blue marble is drawn, there are only two blue marbles and four marbles in total remaining in the bag. Therefore, the probability of drawing a second blue marble is lower than the probability of drawing a blue marble on the first draw. The probability of drawing two blue marbles is calculated as the product of the probability of drawing a blue marble on the first draw and the probability of drawing another blue marble on the second draw, given that the first marble was not replaced.