11. Class A and Class B have an equal number of students, some of whom participate in an extracurricular astronomy club. The number of students from Class A who participate in the astronomy club is exactly one-third of the number of students from Class B who do not participate. The number of students from Class B who participate in the astronomy club is one-fourth of the number of students from Class A who do not participate. What fraction of the number of students from Class B who do not participate is the number of students from Class A who do not participate?
11.【Solution】If the people who did not participate from Class A are reduced by $\frac{1}{4}$, it is the same as the people who did not participate from Class B being reduced by $\frac{1}{3}$. Therefore, the required ratio is: $\left(1-\frac{1}{3}\right) \div\left(1-\frac{1}{4}\right)=\frac{8}{9}$.