1. A cooperative receives apple and grape juice in identical barrels and produces an apple-grape drink in identical cans. One barrel of apple juice is enough for exactly 6 cans of the drink, and one barrel of grape juice is enough for exactly 10 cans. When the recipe for the drink was changed, one barrel of apple juice became enough for exactly 5 cans of the drink. How many cans of the drink will one barrel of grape juice now be enough for? (The drink is not diluted with water.)
1. The first method. For one can of the drink, $\frac{1}{6}$ of a barrel of apple juice and $\frac{1}{10}$ of a barrel of grape juice are used, so the volume of the can is

$$
\frac{1}{6}+\frac{1}{10}=\frac{4}{15}
$$

of the barrel's volume.

After changing the recipe, for one can of the drink, $\frac{1}{5}$ of a barrel of apple juice and $\frac{1}{x}$ of a barrel of grape juice are used, so the volume of the can is

$$
\frac{1}{5}+\frac{1}{x}
$$

of the barrel's volume. Thus, we get the equation:

$$
\frac{1}{5}+\frac{1}{x}=\frac{4}{15}
$$

From this, we find

$$
\frac{1}{x}=\frac{4}{15}-\frac{1}{5}=\frac{1}{15}
$$

Therefore, $x=15$.

The second method. For 30 cans, 5 barrels of apple juice and 3 barrels of grape juice were used. In total, 8 barrels. According to the new recipe, 6 barrels of apple juice will be used for 30 cans. Therefore, 2 barrels of grape juice will be used. Thus, one barrel of grape juice is enough for 15 cans.