Subtracting Integers

Number Line

100

Model on a number line:

-4 - (-2) 

Start at -4 then move 2 spaces to the right. Subtracting=move right. Answer=-2

200

Model on a number line.

-1 - 3

Start at -1 then move 3 spaces to the left. Answer=-4

300

When subtracting a positive number on a number line, which direction do you move?

Left

400

When subtracting a negative number, which direction of you move?

Right

500

Model on a number line.

-3 - (-5)

Start at -3 then move 5 spaces to the right. 

Answer= 2

What Happens?

100

Model -1 - (-4) using counters.

Start with 1 (-). Add 3 zero pairs. Remove 4 (-). Answer=3

200

Model -2 - 1 using counters.

Start with 2 (-). Add 1 zero pair. Remove 1 (+). Answer= -3

300

What is a zero pair?

One positive (+1) counter and one negative (-) counter, together makes 0. 

400

Why might you need to add zero when using counters?

To create enough counters of the type you need to remove without changing the overall value. 

500

Model -2 - (-5) using counters. 

Start with 2 (-). Add 3 zero pairs. Remove 5 (-). Answer=3

Subtraction

100

A student says, "When I subtract, I always move left on a number line." Are they correct?

No. Subtracting a negative means moving right on the number line. 

200

What is -5 - (-3)?

-2

300

What is -2 - 1?

-3

400

What is -1 - 3?

-4

500

What is -1 - (-4)?

3

Challenge

100

Solve:

-3 - 2

-5

200

Solve: 

-5 - (-3)

-2

300

Which is greater?

-2 - 3 or -2 - (-3)

-2 - (-3) =1

-2 - 3 =-5

So -2 - (-3) of greater than -2 - (-3).

400

A student models -1 - (-4). Their answer is 3. Is this correct?

Yes!

500

A student models -2 - (-4). Their answer is 6. Is this correct?

No!