# Adding and subtracting negative numbers

A number line can be used to add and subtract negative numbers.

### Example

What is ?

To add -4 and 5, draw the starting number on a number line and count to the right when adding numbers.

So,

## Subtracting with negative numbers

### Example

What is ?

To subtract 2 from -2, start at -2 on a number line, and count to the left when subtracting numbers.

### Example

What is the difference in temperature between a desert at 40 °C and a mountain top at -2 °C?

, so the difference in temperature between the desert and the mountain top is 42 °C.

To subtract a negative number, count to the right. Subtracting a negative number is like adding a positive number.

### Example

What is ?

To subtract -2 from 4, start at number 4 on a number line, and count to the right. So, .

## Rules for adding and subtracting negative numbers

When two signs are written next to each other, the rules for adding and subtracting numbers are:

• two signs that are different become a negative sign
• two signs that are the same become a positive sign

### Examples

• Same signs give a positive:
• Same signs give a positive:
• Different signs give a negative:
• Different signs give a negative:
Question

Calculate .

Question

Calculate .