Well...if there are 40 schools and each one got 180 applications, that would be 7,200 total applications. If each GC hopeful applied to, say, 5 schools, that would be 7,200/5 = 1,440 applicants. If each school granted 50 interviews, 50 x 40 schools = 2,000 interviews, or 1.39 per applicant. There are some crude assumptions in there (e.g. all schools equally desirable and attract equal number of applicants), the biggest one being all applicants are equally qualified.
If half the applicants were lunkheads and had no business applying, then they should get 0 interviews and the other half twice as many (2 x 1.39).
So the unknown parameter is the percentage of lunkheads applying.....