Operation Review: Simple Subtraction Rule

Lesson Plan - Get It!

Audio:

• 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.

• 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

2. 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.

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.