When Bořek was painting the garage door, he accidentally painted over the scale of the outdoor wall thermometer. However, the mercury tube remained undamaged, so Bořek covered the original scale with a homemade strip. On it, he carefully marked divisions, all of the same size and labeled with numbers. His division, however, had a different size than the original division, which represented one degree Celsius, and he also placed the zero differently than where $0{ }^{\circ} \mathrm{C}$ was. Thus, Bořek began measuring temperature in his own units: borcs. When the thermometer should have indicated a temperature of $11^{\circ} \mathrm{C}$, it showed 2 borcs. When it should have indicated $-4{ }^{\circ} \mathrm{C}$, it showed -8 borcs. What is the temperature in degrees Celsius if Bořek sees a temperature of -2 borcs on his thermometer?

(L. Simünek)
At $11^{\circ} \mathrm{C}$, the thermometer shows 2 boroks. When the temperature drops to $-4{ }^{\circ} \mathrm{C}$, which is a decrease of $15^{\circ} \mathrm{C}$, the thermometer shows -8 boroks, which is 10 boroks less than in the first case. A change of 10 boroks corresponds to a change of $15^{\circ} \mathrm{C}$, so a change of 1 borok represents a change of $1.5^{\circ} \mathrm{C}$. The temperature of -2 boroks, which the problem asks for, is 4 boroks less than the temperature given at the beginning of our solution. Therefore, the temperature of -2 boroks in degrees Celsius is

$$
11-4 \cdot 1.5=5
$$

Another solution. The problem can also be solved graphically, for example, on graph paper:

![](https://cdn.mathpix.com/cropped/2024_04_17_d48c9d3fae9e38272aa2g-1.jpg?height=471&width=417&top_left_y=1415&top_left_x=845)