Subtracting Integers

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Subtracting integers is difficult. This is because it can be hard to understand how we can take away things that already have a minus sign in front of them.

For example, let’s say that your friend owes you five dollars. This means that your financial relationship with them is currently -5. Eg. You have 5 dollars less, because you lent five dollars to them.

When they pay back the five dollars, the 5 dollar debt can be removed like this:

-5 – -5 = 0 debt, which is actually the same as -5 + 5 = 0.

Eg. We take their -5 dollar debt and add the 5 dollars they just gave you and this creates a debt of zero dollars.

SUBTRACTING A NEGATIVE IS ALWAYS THE SAME AS ADDING A POSITIVE.

A subtraction sum is always easier to do when we turn it into an addition sum.
This is what we always do with subtraction questions that involve integers.

WE ALWAYS CHANGE SUBTRACTION INTO ADDING THE OPPOSITE.

This is called the “Adding the Opposite Method”.

Adding the Opposite Method

Add the Opp PPT slide

Integer Addition sums are much easier to do than Subtractions, so we always apply the “Add the Opposite” rule to turn every Subtraction question into an Addition sum.

Keep Flip Change “KFC” Rule

Adding the Opposite can be simplified into what is called the “KFC” Rule.

Int Sub PPT KFC Rule

Example 1

5 – 2 = ?

We know the answer is 3, but let’s prove that KFC works.

Keep the 5 as it is, eg. It stays as +5, which is the same as 5
Flip the Subtract into Add
Change the sign of the 2 so that it becomes -2

Our KFC addition sum is: 5 + -2 which on a number line works out as 3.

Example 2

-5 – 2 = ?

Applying KFC, the -5 stays, and the 2 changes its sign to become -2

The KFC sum is therefore

-5 + -2 which works out as an answer of -7 .

eg. Using the “Cancel Zero Pairs” adding method we have:

Sub Int PPT Ex 1

We set this sum out in our workbook like this:

-5 – 2 = ?
K F C
-5 + -2 = -7

Example 3

-5 – -2 = ?

Applying KFC,
the -2 changes its sign to become 2
and our addition sum is:

-5 + 2 = ?

We can work out the answer to this sum using the canceling zeroes method as follows:

Sub Ints PPT Exmple 2

So the answer to our original question is: -5 – -2 = -3.

We set this sum out in our workbook like this:

-5 – - 2 = ?
K F C
-5 + 2 = -3

Videos About the “KFC” Rule

The following video shows how to use the KFC Rule for Integer subtractions.

Click anywhere on the video image below to launch the video in a new window.

Fake of Schooltube Ints Vid Two

This next video follows on from the previous one and gives some more “KFC” examples.

Click anywhere on the video image below to launch the video in a new window.

Fake of Schooltube Ints Vid Three

Subtracting Integers Car Racing Game

This game starts off with us using the left and right arrow keys to drive our car in a race, and then after a little while we have to stop and do an Integer Subtraction question.

If we get the question right, we get bonus items like a rocket booster pack to fly our car for a while, until the next question comes.

Click on the image below, or the link which follows, to play this game.

Subtracting Integers Car Race Game

http://www.math-play.com/math-racing-subtracting-integers-game/math-racing-subtracting-integers-game.html

Subtracting Integers Fish Game

In this fun game we have to click the letter that is the correct answer, before the fish swims to this correct answer.

Click on the image below, or the link which follows, to play this game.

Subtracting Integers Fish Game

http://www.slidermath.com/integer/SlamnS.shtml

Subtracting Integers Speed Test

This is more of an online speed test than a game.

However, it will certainly improve your Integer Subtraction skills.

Click on the image below, or the link which follows, to play this game.

Once you get onto the the new window screen, scroll down to find the Test.

Sub Integers Speed Test

http://www.basic-mathematics.com/subtracting-integers-game.html

Subtracting Integers Online Quiz

This online test will check how well we know our Integer Subtracting.

Click on the image below, or the link which follows, to play this game.

Once you get onto the the new window screen, scroll down to find the Quiz.

Sub Integers Online Quiz

http://www.aaamath.com/sub65_x4.htm

Related Items

Introduction to Integers
Arranging Integers in Order
Adding Integers Using Number Lines
Adding Integers Using Zero Pairs
Multiplying Integers
Dividing Integers
Integers Order of Operations
Directed Number Integers Games
Integers in the Real World
Integers in Drag Racing

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Enjoy,
Passy

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