1. After another labor season, the electrified part of the Mediterranean Tundra doubled. At the same time, its non-electrified part decreased by $25 \%$. What fraction of the entire Tundra was not supplied with electricity at the beginning of the labor season?
# Solution

Let $x$ and $y$ be the fractions of the electrified and non-electrified parts, respectively. Clearly, $x+y=1$. According to the condition, $2x + 0.75y = 1$. We obtain the equation

$$
x+y=2x+0.75y
$$

from which we can find the ratio

$$
\frac{x}{y}=\frac{1}{4}
$$

Now we can find the required ratio

$$
\frac{y}{x+y}=\frac{1}{x / y+1}=\frac{1}{1 / 4+1}=\frac{4}{5}=0.8=80\%
$$

## Answer: $80\%$