Education Technology

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.

Follow the Activity procedures:

  • 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