To find the experimental probability that the next student to enroll will be an undergraduate student, you can use the formula for probability:
\[ P(\text{undergraduate}) = \frac{\text{Number of undergraduate students}}{\text{Total number of students}} \]
In this case, the number of undergraduate students is 9, and the total number of students is the sum of undergraduate and non-undergraduate students:
\[ \text{Total number of students} = 9 + 9 = 18 \]
Now, plug the numbers into the probability formula:
\[ P(\text{undergraduate}) = \frac{9}{18} \]
Now, simplify the fraction:
\[ P(\text{undergraduate}) = \frac{1}{2} \]
Thus, the experimental probability that the next student to enroll will be an undergraduate student is:
\[ P(\text{undergraduate}) = \frac{1}{2} \]