To calculate the experimental probability of randomly selecting a green marble, you need to know the number of times a green marble was selected during the 40 trials.
The formula for experimental probability is:
\[ \text{Experimental Probability} = \frac{\text{Number of successful outcomes}}{\text{Total number of trials}} \]
Since the specific number of times a green marble was selected is not provided in your question, I cannot compute the exact probability. However, if you have the count of green marbles selected, you can simply plug that number into the formula along with the total of 40 trials.
For example, if a green marble was selected 5 times, the probability would be:
\[ \text{Probability} = \frac{5}{40} = 0.125 \]
If you can provide the number of green marbles selected, I can help you find the exact probability.