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