Calculating Probability of Students' Preferences

In a certain town, a group of students conducted a survey about their preferred extracurricular activities. The results showed the following frequencies:

- 30 students preferred sports.

- 25 students preferred music.

- 20 students preferred arts.

- 15 students preferred science.

- 10 students preferred other activities.

Assuming each student chose only one activity and that the students were randomly selected, what is the probability that a randomly selected student from this group prefers either music or arts?

Express your answer as a simplified fraction.