## Task 4 - 060724

In a cylindrical container (a straight circular cylinder with a horizontal base), there is water. The water level is at $\frac{3}{4}$ of the height of the container. After exactly $2 \frac{1}{2}$ liters of water are poured out of this container, the water level is at $\frac{2}{5}$ of the container's height.

What is the capacity of the container?
The volume (measured in liters) is directly proportional to the height of the container. $\frac{3}{4}$ of the volume decreases to $\frac{2}{4}$ of the volume by pouring out $2 \frac{1}{2}$ liters.

Since $\frac{3}{4}-\frac{2}{5}=\frac{7}{20}$, it follows that $\frac{7}{20}$ of the volume is equal to $2 \frac{1}{2}$ liters. Therefore, the container has a capacity of $\frac{50}{7}$ liters.

Solutions of the II. Round 1966 adopted from [5]

### 4.8.3 III. Round 1966, Class 7