Final answer:
The probability of choosing a green marble after removing one white marble without replacement is 1/2 or 50%.
Step-by-step explanation:
If the first marble chosen was a white marble, the total number of marbles in the box decreases from 39 to 38 because the marble is not replaced. There are still 19 green marbles in the box, so the probability of choosing a green marble on the second draw is the number of green marbles divided by the total number of marbles left in the box. Therefore, the probability of choosing a green marble after one white marble has been removed is:
Probability = Number of green marbles / Total number of marbles left
Probability = 19 / 38
Probability = 1/2 or 50%