Number Line
Model on a number line:
-4 - (-2)
Start at -4 then move 2 spaces to the right. Subtracting=move right. Answer=-2
Model -1 - (-4) using counters.
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.
Solve:
-3 - 2
-5
Model on a number line.
-1 - 3
Start at -1 then move 3 spaces to the left. Answer=-4
Model -2 - 1 using counters.
Start with 2 (-). Add 1 zero pair. Remove 1 (+). Answer= -3
What is -5 - (-3)?
-2
Solve:
-5 - (-3)
-2
When subtracting a positive number on a number line, which direction do you move?
Left
What is a zero pair?
One positive (+1) counter and one negative (-) counter, together makes 0.
What is -2 - 1?
-3
Which is greater?
-2 - 3 or -2 - (-3)
-2 - (-3) =1
-2 - 3 =-5
So -2 - (-3) of greater than -2 - (-3).
When subtracting a negative number, which direction of you move?
To create enough counters of the type you need to remove without changing the overall value.
What is -1 - 3?
-4
A student models -1 - (-4). Their answer is 3. Is this correct?
Yes!
Model on a number line.
-3 - (-5)
Start at -3 then move 5 spaces to the right.
Answer= 2
Model -2 - (-5) using counters.
Start with 2 (-). Add 3 zero pairs. Remove 5 (-). Answer=3
What is -1 - (-4)?
3
A student models -2 - (-4). Their answer is 6. Is this correct?
No!