Åk 6–9
 
English/Soomaali

3.3 Add and Subtract Negative Numbers
When adding and subtracting, we usually put parentheses around the negative numbers in order to clearly show that it is a negative number and not the operation subtraction.





Addition with Negative Numbers 

4 + (-3) = 4 - 3

What happens when the value if we add with a negative number? To add with -3 is the same thing as subtracting by 3.


4 + (-3) = 4 – 3 = 1

When adding by a negative number the value will decrease.  In other words, it is the same thing as subtracting by 3 in the example above.

Let’s take another example:

-4 + (-2) = -4 - 2

We start at the -4 and add by -3.  This becomes the same thing as subtracting by 2.


-4 + (-2) = -4 -2 = -6




 

Subtraction with a Negative Number

5 - (-2) = 5 + 2

What happens to the value if we subtract with a negative number? Subtracting by -2 is the same thing as adding by 2.


5 - (-2) = 5 + 2 = 7

When subtracting with a negative numbers, the value will increase.

Let’s take another example:


(-4) – (-3) = -4 + 3

We start at the -4 and subtract by -3.  This becomes the same thing as adding by 3.




(-4) – (-3) = (-4) + 3 = -1