Lesson 2: Changing Temperatures

Changing Temperatures

Student Summary

If it is $42^\circ\text{F}$ outside and the temperature increases by $7^\circ\text{F}$ , then we can add the initial temperature and the change in temperature to find the final temperature.

$42 + 7 = 49$

If the temperature decreases by $7^\circ\text{F}$ , we can either subtract $42-7$ to find the final temperature, or we can think of the change as $\text-7^\circ\text{F}$ . As in the previous example, we can add to find the final temperature.

$42 + (\text-7) = 35$

In general, we can represent a change in temperature with a positive number if it increases and with a negative number if it decreases. Then we can find the final temperature by adding the initial temperature and the change. If it is $3^\circ\text{F}$ and the temperature decreases by $7^\circ\text{F}$ , then we can add to find the final temperature.

$3+ (\text-7) = \text-4$

We can represent signed numbers with arrows on a number line. We can represent positive numbers with arrows that start at 0 and point to the right. For example, this arrow represents +10 because it is 10 units long and it points to the right.

A number line with the numbers negative 10 through 10 indicated. An arrow starts at 0, points to the right, and ends at 10.There is a solid dot indicated at 10.

We can represent negative numbers with arrows that start at 0 and point to the left. For example, this arrow represents -4 because it is 4 units long and it points to the left.