## Lesson: Adding and Subtracting With Negative Integers Introducing the Concept

Your students have worked with adding and subtracting integers on a number line, but it is a good idea to start by reviewing the basic skills of adding and subtracting on a number line. This will provide a visual model of what they are doing and should help them understand and remember the rules.

Materials: a large number line on the chalkboard or on an overhead transparency

Prerequisite Skills and Concepts: Students should know how to add and subtract positive numbers using a number line.

• Point to various points on the number line and Ask: What is this point? What is this point? What kinds of points lie to the left of zero on the number line?
• Ask: Who would like to come up and show us how to add 5 + 3 using the number line?
• Ask: Who would like to come up and show us how to add 5 +-3 on the number line?
You may need to demonstrate this. Explain that you start with the 5 and then go the directed distance of the number that follows when adding, in this case   -3 units or 3 units to the left.

Have students do the following examples of adding integers at their desks, and then have volunteers demonstrate the solutions for the class: 3 + (-7); -4 + (-3); -5 + 7; -6 + 2; 8 + (-4). Put a list of all the problems done on the board off to the side for students to refer to as you ask the following questions.

• Ask: If we add two negative integers, is the sum positive or negative? If we add two positive integers, is the sum positive or negative?
• Ask: If I add a positive integer and a negative integer, how can I tell if the sum is positive or negative?
Stress that the sign of the sum of a positive integer and a negative integer depends on which number is farther from zero.