# Lesson 7

Changing Elevation

### Lesson Narrative

In this lesson, students build towards fluency with adding signed numbers. They begin with the concrete context of elevations above and below sea level, but then move to more abstract work. They see that adding a number and its opposite gives a sum of 0. They contrast adding numbers with the same sign with adding numbers with different signs. Using the structure of opposites on the number line, they see that when adding two numbers with different signs, the sign of the sum will match the sign of the addend with the greater magnitude (MP7).

Teacher Notes for IM 6–8 Accelerated
The term “opposite” was introduced previously. This lesson extends the concept further. Replace the existing learning goal about comprehending this term with the new goal “Describe (in writing) what would be considered the opposite value in a given situation.”

### Learning Goals

Teacher Facing

• Comprehend the term “opposite” (in spoken and written language) refers to numbers with the same magnitude but different signs.
• Create and interpret equations and diagrams that represent adding signed numbers in the context of elevation.
• Generalize (orally) a method for determining the sum of two signed numbers.

### Required Preparation

For optional activity, cut one strip of receipt tape, for every 2 students. Each strip of receipt tape should be at least 4 feet long. You may want to prepare some strips that are even longer, in case groups choose extra long objects.

### Student Facing

• I understand how to add positive and negative numbers in general.

Building On