Answer:
81.4% probability that a freshman selected at random from this group is enrolled in an economics and/or a mathematics course
Explanation:
A probability is the number of desired outcomes divided by the number of total outcomes.
Total outcomes:
500 freshmen
Desired outcomes:
Enrolled in an economics and/or a mathematics course
Build the Venn's diagram.
I am going to say that:
A is the number of students enrolled in the economics course.
B is the number of students enrolled in the mathematics course.
We have that:

In which a is the number of students who are enrolled in the economics course but not mathematics and
is the number of students enrolled in both those courses.
By the same logic, we have that:

129 are enrolled in both an economics and a mathematics course.
This means that
.
216 are enrolled in a mathematics course
This means that




320 are enrolled in an economics course
This means that




We want

Probability:

81.4% probability that a freshman selected at random from this group is enrolled in an economics and/or a mathematics course