# Lesson 1

Positive and Negative Numbers

## 1.1: Notice and Wonder: Memphis and Bangor (5 minutes)

### Warm-up

The purpose of this task is to introduce students to temperatures measured in degrees Celsius. Many students have an intuitive understanding of temperature ranges in degrees Fahrenheit that are typical of the city or town in which they live, but many are unfamiliar with the Celsius scale.

### Launch

Arrange students in groups of 2. Tell students that they will look at an image, and their job is to think of at least one thing they notice and at least one thing they wonder. Display the image for all to see. Ask students to give a signal when they have noticed or wondered about something. Give students 1 minute of quiet think time, and then 1 minute to discuss the things they notice with their partner, followed by a whole-class discussion.

### Student Facing

What do you notice? What do you wonder?

### Activity Synthesis

Ask students to share the things they noticed and wondered. Record and display their responses for all to see. If possible, record the relevant reasoning on or near the image. After each response, ask the class if they agree or disagree and to explain alternative ways of thinking, referring back to the images each time. Explain to students that temperatures are usually measured in either degrees Fahrenheit, which is what they are probably most familiar with, and degrees Celsius, which may be new for them. Tell them that many other countries measure temperature in degrees Celsius and that scientists use this temperature scale. One thing that is special about the Celsius scale is that water freezes at 0 degrees and boils at 100 degrees (at sea level).

## 1.2: Above and Below Zero (10 minutes)

### Activity

The purpose of this task is to understand that there are natural mathematical questions about certain contexts for which there are no answers if we restrict ourselves to positive numbers. The idea is to motivate the need for negative numbers and to see that there is a natural representation of them on the number line. This task is not about operations with signed numbers, but rather why we extend our number system beyond positive numbers. Students reason abstractly and quantitatively when they represent the change in temperature on a number line (MP2).

### Launch

Display this image for all to see.

Tell students, “The thermometer showed a temperature of 7 degrees Celsius one morning. Later, the temperature increased 4 degrees. We can represent this change in temperature using a number line, as shown in the picture.”

Arrange students in groups of 2. Give students 2 minutes of quiet work time for question 1. Give students 2 minutes to compare their responses to their partners and to work on question 2.

Students using the digital version of the curriculum can explore the changes in temperature with the dynamic applet.

Reading: MLR6 Three Reads. Use this routine to support students’ comprehension of the temperature changes for the first situation. In the first read, students read the situation with the goal of comprehending the text (e.g., the thermometer was at a certain temperature earlier in the day and then changed later in the day). Delay asking “What was the temperature late in the afternoon?”. In the second read, ask students to analyze the text to understand the quantities (e.g., at noon, the temperature was 7 degrees Celsius; it increases 6 degrees by late afternoon). In the third read, direct students’ attention to the question and ask students to brainstorm possible mathematical solution strategies to answer the question.
Design Principle(s): Support sense-making

### Student Facing

1.  Here are three situations involving changes in temperature. Represent each change on the applet, and draw it on a number line. Then, answer the question.

1. At noon, the temperature was 5 degrees Celsius. By late afternoon, it has risen 6 degrees Celsius. What was the temperature late in the afternoon?

2. The temperature was 8 degrees Celsius at midnight. By dawn, it has dropped 12 degrees Celsius. What was the temperature at dawn?

3. Water freezes at 0 degrees Celsius, but the freezing temperature can be lowered by adding salt to the water. A student discovered that adding half a cup of salt to a gallon of water lowers its freezing temperature by 7 degrees Celsius. What is the freezing temperature of the gallon of salt water?

2.  Discuss with a partner:

1. How did you name the resulting temperature in each situation? Did both of you refer to each resulting temperature by the same name or different names?

2. What does it mean when the resulting temperature is above 0 on the number line? What does it mean when a temperature is below 0?

3. Do numbers below 0 make sense outside of the context of temperature? If you think so, give some examples to show how they make sense. If you don’t think so, give some examples to show otherwise.

### Launch

Display this image for all to see.

Tell students, “The thermometer showed a temperature of 7 degrees Celsius one morning. Later, the temperature increased 4 degrees. We can represent this change in temperature using a number line, as shown in the picture.”

Arrange students in groups of 2. Give students 2 minutes of quiet work time for question 1. Give students 2 minutes to compare their responses to their partners and to work on question 2.

Students using the digital version of the curriculum can explore the changes in temperature with the dynamic applet.

Reading: MLR6 Three Reads. Use this routine to support students’ comprehension of the temperature changes for the first situation. In the first read, students read the situation with the goal of comprehending the text (e.g., the thermometer was at a certain temperature earlier in the day and then changed later in the day). Delay asking “What was the temperature late in the afternoon?”. In the second read, ask students to analyze the text to understand the quantities (e.g., at noon, the temperature was 7 degrees Celsius; it increases 6 degrees by late afternoon). In the third read, direct students’ attention to the question and ask students to brainstorm possible mathematical solution strategies to answer the question.
Design Principle(s): Support sense-making

### Student Facing

1. Here are three situations involving changes in temperature and three number lines. Represent each change on a number line. Then, answer the question.

1. At noon, the temperature was 5 degrees Celsius. By late afternoon, it has risen 6 degrees Celsius. What was the temperature late in the afternoon?
2. The temperature was 8 degrees Celsius at midnight. By dawn, it has dropped 12 degrees Celsius. What was the temperature at dawn?

3. Water freezes at 0 degrees Celsius, but the freezing temperature can be lowered by adding salt to the water. A student discovered that adding half a cup of salt to a gallon of water lowers its freezing temperature by 7 degrees Celsius. What is the freezing temperature of the gallon of salt water? 2. Discuss with a partner:

1. How did each of you name the resulting temperature in each situation?

2. What does it mean when the temperature is above 0? Below 0?

3. Do numbers less than 0 make sense in other contexts? Give some specific examples to show how they do or do not make sense.

### Anticipated Misconceptions

Some students may have difficulty representing change on the number line. Students sometimes count tick marks rather than counting the space between tick marks when working on a number line. For example, in the original problem image, the arrow on the number line represents a change of 4 degrees. Some students may begin at tick mark 7 and count the tick marks to yield a temperature change of 5 degrees. When reviewing that task with the whole class, be sure to make this important point and demonstrate counting on a number line by highlighting the space between the tick marks while counting out loud.

### Activity Synthesis

Some students will use the phrase “degrees below zero.” Use this activity to introduce the term negative as a way to represent a quantity less than zero. In contrast, ask students how they would describe a quantity that is greater than zero on the number line. Some students will have a pre-existing understanding of positive and negative numbers. Discuss the use of + and - as symbols to denote positive and negative numbers. Notation will be important throughout the rest of this unit. Students should understand that +7 and 7 both represent positive 7. Negative 7 is represented as -7.

Representation: Develop Language and Symbols. Create a display of important terms and vocabulary. Invite students to suggest language or diagrams to include that will support their understanding of: negative.
Supports accessibility for: Conceptual processing; Language; Memory

## 1.3: High Places, Low Places (20 minutes)

### Activity

The purpose of this task is to present a second, natural context for negative numbers and to start comparing positive and negative numbers in preparation for ordering them. Monitor for students who make connections between elevation and temperature or come up with strategies for deciding which points are lower or higher than other points. Students may use the structure of a vertical number line in order to compare the relative location of each elevation (MP7).

### Launch

Display the table of elevations for all to see. Ask students to think of a way to explain in their own words what the numbers mean. Ask two or three students to share their ideas.

Tell students, “The term ‘elevation’ is commonly used to describe the height of a place (such as a city) or an object (such as an aircraft) compared to sea level. Denver, CO, is called ‘The Mile High City’ because its elevation is 1 mile or 5,280 feet above sea level.”

Arrange students in groups of 2 and give students 5 minutes of quiet work time to answer the first five questions. Ask students to be prepared to explain their thinking in a whole-class discussion.

Students using the digital activity are provided with an interactive map in addition to the questions about elevation. After they complete the questions in the task, they can drag each point to the elevation on the number line for the landmark it represents.

Action and Expression: Internalize Executive Functions. Chunk this task into more manageable parts. Check in with students after the first 2–3 minutes of work time. Check to make sure students have attended to all parts of the original figures.
Supports accessibility for: Organization; Attention
Reading, Writing, Speaking: MLR5 Co-Craft Questions. To help students use language related to positive and negative numbers within the context of elevation, show students the table and ask pairs to write down mathematical questions to ask about the situation. Have students share their questions with a partner and then share out with the class.
Design Principle(s): Support sense-making

### Student Facing

1. Here is a table that shows elevations of various cities.

city elevation (feet)
Harrisburg, PA 320
Bethell, IN 1,211
Denver, CO 5,280
Coachella, CA -22
Death Valley, CA -282
New York City, NY 33
Miami, FL 0
1. On the list of cities, which city has the second highest elevation?
2. How would you describe the elevation of Coachella, CA, in relation to sea level?
3. How would you describe the elevation of Death Valley, CA, in relation to sea level?
4. If you are standing on a beach right next to the ocean, what is your elevation?
5. How would you describe the elevation of Miami, FL?
6. A city has a higher elevation than Coachella, CA. Select all numbers that could represent the city’s elevation. Be prepared to explain your reasoning.

1. -11 feet
2. -35 feet
3. 4 feet
4. -8 feet
5. 0 feet
2. Here are two tables that show the elevations of highest points on land and lowest points in the ocean. Distances are measured from sea level. Drag the points marking the mountains and trenches to the vertical number line and answer the questions.

point mountain continent elevation (meters)
C Everest Asia 8,848
H Kilimanjaro Africa 5,895
E Denali North America 6,168
A Pikchu Pikchu South America 5,664
point trench ocean elevation (meters)
F Mariana Trench Pacific -11,033
B Puerto Rico Trench Atlantic -8,600
D Tonga Trench Pacific -10,882
G Sunda Trench Indian -7,725

1. Which point in the ocean is the lowest in the world? What is its elevation?
2. Which mountain is the highest in the world? What is its elevation?
3. If you plot the elevations of the mountains and trenches on a vertical number line, what would 0 represent? What would points above 0 represent? What about points below 0?
4. Which is farther from sea level: the deepest point in the ocean, or the top of the highest mountain in the world? Explain.