The number line
- Numbers to the left on a number line are smaller: −5 is less than −2, which is less than 0.
- Negative numbers are used for temperatures below zero, bank overdrafts and depths below sea level.
Adding and subtracting
- Use a number line: 3 − 7 = −4, and −2 + 5 = 3, and −3 − 4 = −7.
- Subtracting a negative is the same as adding: 5 − (−2) = 5 + 2 = 7.
- Adding a negative is the same as subtracting: 6 + (−4) = 6 − 4 = 2.
- A temperature change from −6 °C to 4 °C is a rise of 10 °C.
Multiplying and dividing
- Two signs the same give a positive answer: −3 × −4 = 12, and −20 ÷ −5 = 4.
- Two different signs give a negative answer: 5 × −2 = −10, and −12 ÷ 3 = −4.
- Squaring a negative number gives a positive answer: (−3)² = 9. Cubing it gives a negative answer: (−2)³ = −8.
Key terms
- Negative number
- A number less than zero.
- Positive number
- A number greater than zero.
- Number line
- A line showing numbers in order, used to add and subtract.
- Integer
- A whole number, which can be positive, negative or zero.
- Difference
- How far apart two numbers are.
- Inverse
- The opposite operation: subtracting undoes adding.