In a tournament, how many students participated in both Mathematics and Science?

To determine how many students participated in both Mathematics and Science, one would typically need information regarding the total number of students in both subjects, as well as any overlaps between the two groups.

The choice indicating that 18 students participated in both subjects suggests a specific intersection between the two groups of participants. In scenarios involving sets, the principle is that the number of participants in both subjects would reflect the overlap of those who are counted in each individual subject's total.

This correctly points to the necessity of understanding how subsets interact within a larger set. Use of data such as a Venn diagram can visually represent the situation, allowing a clearer view of student distribution across the two subjects. An essential fact to emphasize is that the figure indicating 18 represents a logical count grounded in the given data, showcasing students active in both areas.

Without additional context from the problem, one can affirm that the number aligns with a plausible intersection of participants based on typical outcomes in a scenario of this nature.