5.2.1 Negative Numbers on a Thermometer

Throughout our work, negative numbers will be denoted by using a raised negative () sign to distinguish it from the subtraction sign (−). (You will notice that in other textbooks and material, this distinction is not always made, and the same subtraction symbol is often used for both negative numbers and the subtraction operator.)

This shows a fridge thermometer with a scale marked in one degree C intervals from –30 °C to 40 °C. The bar of mercury stops at –4 °C. Shading shows that the three-star rating applies to temperatures from –30 °C to two intervals to the right of –20°C, the two-star rating to temperatures from the end of the three-star rating to two intervals to the right of –10 °C and the one-star rating to temperatures from –8 °C to zero.

Another common unit that is used to measure temperature is degrees Celsius (ºC). You can check the temperature of a fridge or freezer using a special thermometer which shows the temperature between about 30 ºC and 40 ºC. On the thermometer, the marks above each of the small divisions represents one degree C. This means that the temperature recorded is 4 ºC. You can see on the thermometer that the temperature increases to the right and decreases to the left.

Activity symbol Activity: Freezer Stars

On the thermometer above, what is the temperature range that corresponds to two stars and three stars?

Hint symbol


You could draw the thermometer in your math notebook and mark the corresponding ranges. Remember that numbers to the left of zero have a negative sign, and become more negative as you move to the left. For example, 10 ºC is to the left of 4 ºC.

Solution symbol


The two stars symbol corresponds to a temperature range from 18 ºC to 8 ºC.

The three stars mark from 30 ºC to 18 ºC.

If you would like a little more practice getting comfortable with negative numbers, check out this website [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] .

5.2 Negative Numbers

5.2.2 Uses of Negative Numbers