Operation Review: Simple Subtraction Rule

Contributor: Briana Pincherri. Lesson ID: 11181

Do you have negative feelings about subtraction, especially when negative numbers are involved? Learn the easy rules to turn those negatives into a positive math experience!



learning style
personality style
Lion, Otter
Grade Level
Middle School (6-8)
Lesson Type
Skill Sharpener

Lesson Plan - Get It!

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  • How do you feel about subtracting positive and negative numbers in the same problem?
  • Does it make your head spin?

Well, good news! When those pesky positive and negative signs appear in the same subtraction problem, you can change the problem to addition and solve it!

It's true, and this lesson shows you how to do it!

  • Are you ready for this?

If you know how to complete addition problems with positive and negative signs, then you can easily subtract as well.

  • How?

Nearly every subtraction problem involving positive and negative numbers can be rewritten as an addition problem.

Take a look.

SIMPLE SUBTRACTION ALERT: You can rewrite these as addition problems.

  -4 - (-3) = -1 is the same as -4 + 3 = -1
   5 - 8 = -3 is the same as  5 + (-8) = -3
  -4 - 2 = -6 is the same as -4 + (-2) = -6


  • Do you see how the subtraction problems on the left were just rewritten as addition problems on the right?

Pretty neat! This is possible because of two rules.

  1. Two negative signs side by side make a positive.

Example: -(-3) = +3

  1. When subtracting a number, it is the same as adding the negative version of the number.

Example: – 5 = +(-5)

Take a moment to consider this.

  • What about -7 - (-8)?
  • Could you change this one to an addition problem?

The problem –7 - (-8) sure has a lot of negative signs, but that does not matter.

You can change it to an addition problem by recognizing that two negatives side by side in a row (the -(-8) in this problem) will make a positive.

This changes the problem to –7 + 8.

Now, follow the rules of addition.

  • Same signs ADD and keep the same sign.
  • Different signs SUBTRACT and keep the sign of the bigger number.

This answer would be –7 + 8 = 1.

Work through a few more examples with the video below.

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Hopefully, this has your mind saying, "WOW! Subtraction sure is simple because it just becomes addition!"

Now, go ahead and move to the Got It? section to test your understanding a little further and see if this is all adding up.

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