Use Negative Numbers in Context and Calculate Intervals Across Zero 6 - Reasoning

In the context of understanding negative numbers and calculating intervals across zero, a practical example is provided using temperature changes over time in Helsinki, Finland. Tia observes that at 4 p.m., the temperature is a chilly −11°C. To determine the temperature at 2 p.m., we need to consider the recorded changes in temperature during the two hours leading up to 4 p.m. According to the data, from 2 p.m. to 3 p.m., there was a rise in temperature of 3°C, followed by a decrease of 5°C from 3 p.m. to 4 p.m.

Working backwards from 4 p.m., we add the 5°C difference to the −11°C, which gives us −6°C at 3 p.m. Then, from 3 p.m. to 2 p.m., we factor in the increase in temperature of 3°C. By adding this increase to the −6°C at 3 p.m., we find that the temperature at 2 p.m. was −9°C. This exercise demonstrates how to use negative numbers in a real-life context and how to calculate intervals that cross the zero point on the temperature scale.