Materials

Standards

  • MP.2

  • Apply and extend previous understandings of numbers to the system of rational numbers.

  • Apply and extend previous understandings of operations with fractions to add, subtract, multiply, and divide rational numbers.

Objectives

  • Use a number line to subtract integers

  • Use addition of opposite integers to find the difference between two integers Key Concept

Key Concept

  • Subtract two integers by adding the opposite of the integer that is being subtracted

Vocabulary

Tier 2 Point
Solve
Tier 3 Tic Mark

Before Lesson

Give students opportunities to demonstrate proficiency in adding positive and negative integers before starting this lesson.

Background

Help students begin to recognize that subtracting integers is an extension of adding integers. Ask students what the relationship is between addition and subtraction (they are opposite operation). Have them predict how subtracting integers will relate to adding integers.

Guided Practice

  • Use a Number Line to Subtract Integers
  • Use Addition to Subtract Integers

Core Skill

Perform Operations: Read the text with students, helping them understand that subtracting one number from another is the same as adding the opposite of the number. For example, write the problems 5-2 and 5+(-2) on the board. Draw a number line from 0 to 5 beneath the problems. Use the number line to demonstrate how the second problem is the same as the first, and the answer is the same. Next, have students complete the activity presented in the last paragraph of the sidebar. Encourage students to share their number lines and explanations with the class.

Represent Real-World Problems: After reading the sidebar, encourage students to work together to solve the problem. Have them draw a number line from -15 to +15 to model the solution. Allow students to find another way to solve the problem, too, such as drawing a picture. Afterward, encourage students to share the model they used to solve the real-world problem.

Extension

Make Connections: Pair English language learner with fluent English speakers to discuss how subtracting integers is similar to and different from adding integers and subtracting whole numbers. Encourage students to use lesson vocabulary as much as possible.

Explain Phenomena in Terms of Concepts: Have students’ research weather records in any location of interest that has records going back at least five decades. Ask students to determine the record highs and lows for each decade, and calculate the variation between the two. Then have them explain the variations in the context of the principle of positive and negative integers.