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by Brigid Del Carmen
Topics: Middle School, Math

Positive or negative numbers, called integers, can pop up anytime, anywhere in middle school math. Understanding how to add and subtract integers can be a challenge at first, but once you know how to handle the heat, it's a breeze! Remember when your middle schooler was a kindergartener and learned 2+2=4 using Cheerios? The same idea can be used with integers, however the Cheerios are now coins and the process requires a couple more steps!

What You Need:
  • 10 pennies
  • 10 nickels
  • pencil
  • paper

What You Do:

  1. Place 10 pennies and 10 nickels on the table. Explain that the pennies represent positive integers and the nickels represent negative integers.
  2. Write a simple addition problem using integers:

    3. (5) + (-3) =

  3. Place 5 pennies in a line and 3 nickels underneath the pennies.

     

    P P P P P

    N N N

  4. Place the 3 nickels on top of 3 pennies. Explain how positive and negative integers cancel each other out, and ask “What do you have left?” (Answer: 2 pennies, or positive 2)
  5. Repeat the process using different addition problems:

    (2) + (-6) =

    P P

    N N N N N N

    Place 2 pennies on top of 2 nickels. Ask “What do you have left?” (Answer: 4 nickels, or negative 4)

    (-2) + (-6) =

    N N

    N N N N N N

    In this case, point out that there are no pennies (positives) to cancel out the nickels (negatives), so you can just add up the nickels. (Answer: 8 nickels, or negative 8)

  6. Now that you've got adding integers covered, it's time to subtract! Subtracting integers is all about changing the signs first. For example:

    4 – (-1) becomes 4 + (+1)

    Show coins

    Answer: 5 pennies (5)

    (-4) – (1) becomes (-4) + (-1)

    Show coins

    Answer: 5 nickels (-5)

    (-4) – (-1) becomes (-4) + (+1)

    Show coins

    Answer: 3 nickels (-3)

Tips:

  1. Always use the new term “integer” rather than “number”.
  2. Demonstrate the process 1-2 times, then do the process with your child. Next, have your child solve problems on her own and finally, have your child “teach” the process to someone else in your house!