## Negative numbers

Negative numbers are numbers below zero!

Examples of negative numbers are:
• Temperatures in the winter. (brrr!)
• Altitudes below sea level.
The numbers you call whole numbers will now be called positive whole numbers, (+1,+4,+5).

The positive numbers, the negative numbers and zero together are called integers.

You can picture integers on a number line, like this one:
``` ...---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|...
-7  -6  -5  -4  -3  -2  -1   0  +1  +2  +3  +4  +5  +6  +7  +8
```
You can think of adding and subtracting as moving along this line.
You move left to subtract, and you move right to add.

ADDING: Start at the first number and move right the second number of places:

Example: -3 +5
```                       o----- 5 moves ----->
start-> o---|---|---|---|---|
...---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|...
-7  -6  -5  -4  -3  -2  -1   0  +1  +2  +3  +4  +5  +6  +7  +8
^
```
SUBTRACTING: Start at the first number and move left the second number of places:

Example: +2 - 4
```                           <--- 4 moves ---o
|---|---|---|---o <- start
...---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|...
-7  -6  -5  -4  -3  -2  -1   0  +1  +2  +3  +4  +5  +6  +7  +8
^