Unit 5, Lesson 2
Changing Temperatures
Grade 7
2.1
Warm-up
Which three go together? Why do they go together?
- Number line. 21 evenly spaced tick marks. Scale negative 10 to 10, by 1's. Two arrows. One arrow points to the right from 0 to 3. One arrow points to the right from 3 to 7.
- Number line. 21 evenly spaced tick marks. Scale negative 10 to 10, by 1's. Two arrows. One arrow points to the right from 0 to 3. One arrow points to the left from 3 to negative 6.
- Number line. 21 evenly spaced tick marks. Scale negative 10 to 10, by 1's. Two arrows. One arrow points to the right from 0 to 3. One arrow points to the left from 3 to 0.
- Number line. 21 evenly spaced tick marks. Scale negative 10 to 10, by 1's. Two arrows pointing to the left, one from 0 to negative 4 and another from negative 4 to negative 9.
2.2
Activity
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Complete the table, and draw a number line diagram for each situation.
start () change () final () addition equation a +40 10 degrees warmer +50 b +40 5 degrees colder c +40 30 degrees colder d +40 40 degrees colder e +40 50 degrees colder -
Complete the table, and draw a number line diagram for each situation.
start () change () final () addition equation a -20 30 degrees warmer b -20 35 degrees warmer c -20 15 degrees warmer d -20 15 degrees colder
Student Lesson Summary
If it is outside and the temperature increases by , then we can add the initial temperature and the change in temperature to find the final temperature.
If the temperature decreases by , we can either subtract to find the final temperature, or we can think of the change as . As in the previous example, we can add to find the final temperature.
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 and the temperature decreases by , then we can add to find the final temperature.
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.
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.
To represent addition, we put the arrows “tip to tail.” So this diagram represents :
A number line with the numbers negative 10 through 10 indicated. An arrow starts at 0, points to the right, and ends at 3. A second arrow starts at 3, points to the right, and ends at 8. there is a solid dot indicated at 8.
And this diagram represents :
A number line with the numbers negative 10 through 10 indicated. An arrow starts at 0, points to the right, and ends at three. A second arrow starts at 3, points to the left, and ends at negative 2. There is a solid dot indicated at negative.
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