Of all the students in a certain dormitory,$$\frac{1}{2}$$ are first-year students and the rest are
second-year students. If $$\frac{4}{5}$$ of the first-year students have not declared a major and if the
fraction of second-year students who have declared a major is 3 times the fraction of
first-year students who have declared a major, what fraction of all the students in the
dormitory are second-year students who have not declared a major?
答案：B