Answer:
There is a probability of 0 that the student plays both string and brass.
Step-by-step explanation:
Looking at the universal set, there are 40 students at this high school, 15 of which play string, 20 play brass, and 5 play neither (probably drummers). Note how there is no intersection of A and B, which is the probability we are looking for.
Since there is no intersection in the universal set between subset A and subset B, you can say that there is a probability of 0 since there is no overlap between the two subsets.
Cheers.