2. To fight against the mice, the cat Leopold must drink animalin daily. The cat has a bottle of animalin solution in water (a colorless transparent liquid) with a volume of $V=0.5$ l and a volumetric concentration of animalin $C_{0}=40 \%$. Every day, Leopold drinks $v=50$ ml of the solution, and to avoid being noticed by the mice, he adds the same volume of water to the bottle. Find the volumetric concentration of animalin in the bottle after the cat has drunk $n=5$ times, each time $v=50$ ml of liquid, and after each time, added water to the bottle.
2. Let's find the change in the concentration of the absinthe solution after the cat drinks one portion. By definition of volume concentration,

$$
C_{0}=\frac{v_{O}}{V}
$$

where $C_{0}$ is the volume concentration of the solution, $v_{o}$ is the initial volume of absinthe in the bottle, and $V$ is the total volume of the solution. Therefore, after the cat drinks $v$ ml of the solution, the remaining volume of absinthe is

$$
v_{O}^{\prime}=C_{0}(V-v)
$$

Since the volume of the solution returns to $V$ after adding water, the new volume concentration of the solution $C_{1}$ is

$$
C_{1}=\frac{v_{o}^{\prime}}{V}=\frac{C_{0}(V-v)}{V}=C_{0}\left(1-\frac{v}{V}\right)
$$

After the cat drinks the second portion of absinthe, the concentration in the solution is found similarly:

$$
C_{2}=C_{1}\left(1-\frac{v}{V}\right)=C_{0}\left(1-\frac{v}{V}\right)^{2}
$$

Therefore, after the cat drinks $n$ portions of absinthe (refilling the bottle with water after each drink), the concentration of absinthe in the bottle will be

$$
C_{5}=C_{0}\left(1-\frac{v}{V}\right)^{n}=23.6 \%
$$