The wolves were pressing apple cider. They had it in two containers of the same volume, with almost the same amount in both. If they poured 1 liter from the first to the second, they would have the same amount in both, but neither container would be full. So they decided to pour 9 liters from the second to the first. Then the first container was completely full, and the cider in the second filled exactly one-third of its volume. How many liters of cider did they press, what was the volume of the containers, and how much cider was in them originally?

(M. Volfová)
Let the number of liters in the first barrel before pouring be $x$, and in the second barrel be $y$. After pouring one liter, there would be $x-1$ liters in the first barrel and $y+1$ liters in the second barrel, and it would hold that

$$
x-1=y+1 \text {. }
$$

After pouring 9 liters, there would be $x+9$ liters in the first barrel, which would be full, and $y-9$ liters in the second barrel, which would constitute one-third of the barrel's volume, i.e., one-third of what was in the first barrel. Therefore,

$$
x+9=3 \cdot(y-9) \text {. }
$$

From the first equation, we can express $x=y+2$ and substitute it into the second: $y+2+9=3 y-27$. After rearranging, we get $y=19$ and $x=21$.

There were originally 21 liters in the first barrel and 19 liters in the second barrel of must, and Vlček and his friends tapped a total of 40 liters of must. The volume of each of the two barrels was 30 liters.