A3. In the herd, there are deer and roe deer. Roe deer represent $55 \%$ of the herd, and their mass represents $45 \%$ of the total mass of the herd. What is the ratio between the average mass of a deer and the average mass of a roe deer?
(A) $\frac{81}{40}$
(B) $\frac{3}{2}$
(C) $\frac{121}{81}$
(D) $\frac{11}{9}$
(E) $\frac{6}{5}$
A3. In the barn, there are $x$ animals with a total weight of $y$. Then, in the barn, there are $\frac{55}{100} x$ rabbits with a total weight of $\frac{45}{100} y$ and $\frac{45}{100} x$ deer with a total weight of $\frac{55}{100} y$. The average weight of a rabbit is thus $\frac{45}{100} y : \frac{55}{100} x = \frac{9 y}{11 x}$, and the average weight of a deer is $\frac{55}{100} y : \frac{45}{100} x = \frac{11 y}{9 x}$. The average weight of a deer is thus $\frac{11 y}{9 x} : \frac{9 y}{11 x} = \frac{121}{81}$ times greater than the average weight of a rabbit. The correct answer is $C$.