# Activities

• • • ##### Subject Area

• Math: Middle Grades Math: Number Sense

• ##### Author 6-8

60 Minutes

• ##### Device
• TI-73 Explorer™

TI Connect™

• ##### Accessories

TI Connectivity Cable

• ##### Other Materials
This is Activity 2 from the EXPLORATIONS Book:
Walking the Line: Activities for the TI-73 Number Line.

## Integer Subtraction--What's the Difference?

#### Activity Overview

In this activity, students use the number line to investigate subtraction of integers and to justify and support the rules they develop.

#### Before the Activity

• Access the NUMLINE application. and set up a number line with minimum value -40, maximum value 40, scale 5, and starting point 0
• See the attached PDF file for detailed instructions for this activity
• Print pages 17 - 22 from the attached PDF file for your class

#### During the Activity

Distribute the pages to the class.

• Add a positive integer and a negative integer x + (- y ), where x > y, and observe that the vectors on the number line point in opposite directions
• Subtract y directly from x, x - y, where x > y, and observe that the vectors point in opposite directions
• Observe that adding a negative integer to a positive integer looks just like subtracting a positive integer from a positive integer
• Compute x + (- y) and y - x, where y > x and note the result
• Note that subtracting a number is the same as adding the opposite number
• x - y = x + (- y)
• x - (- y) = x + y
• Verify these statements with the calculator and solve similar problems
• #### After the Activity

Students complete the Student Activity sheet.

Review student results:

• As a class, discuss questions that appeared to be more challenging
• Re-teach concepts as necessary