Numbers & the number system
More on negative numbers
Negative numbers are numbers less than zero. We use them in real life to describe things like very cold temperatures and positions below sea level.
Reading and writing negative numbers
A number less than zero has a minus sign in front of it. We say −6 as 'negative six'. On a number line the negative numbers go to the LEFT of zero: −1, −2, −3, and so on.
Negative numbers in the real world
Negative numbers describe a very cold temperature, such as −4 °C, or a position below sea level, such as −30 m for 30 metres below the surface. An iceberg has much more ice below sea level than above it.
Colder and warmer
On a number line, the further LEFT a number is, the colder it is. So −6 °C is colder than −2 °C, and −5 °C is colder than −4 °C. Be careful: with negatives, a bigger digit can mean a colder temperature.
Counting on and back through zero
To find a colder temperature, jump back (left). To find a warmer temperature, jump on (right). Warmer than −4 by 6 degrees: −4 + 6 = 2. Colder than 5 by 9 degrees: 5 − 9 = −4. A number line makes these jumps easy to see.
Worked examples
A colder temperature
- England is 11 °C; Iceland is 15° colder.
- Draw a number line and start at 11.
- Colder means jump back 15 places: 11 − 15.
Answer: The temperature in Iceland is −4 °C.
A warmer temperature
- Start at −4 °C.
- Warmer by 6 degrees means jump on 6 places.
- −4 + 6 = 2.
Answer: It is 2 °C.
Which is coldest
- Compare −6 °C, 0 °C, 1 °C and −2 °C.
- The one furthest to the left on the number line is coldest.
- −6 is furthest left.
Answer: −6 °C is the coldest.
Below sea level
- A diver is at −20 m below sea level.
- Rising means jump up (towards zero) by 8.
- −20 + 8 = −12.
Answer: The diver is now at −12 m.
Where you see this in real life
- Reading a very cold temperature such as −10 °C in winter.
- Describing a diver or an iceberg below sea level with a negative number.
- The coldest inhabited place, Oymyakon, once reached −67 °C.
Key words
- Negative number
- A number less than zero, written with a minus sign, such as −6.
- Zero
- The number between the positive and negative numbers.
- Sea level
- The level of the sea, counted as zero; below it is negative.
- Number line
- A line with numbers in order that helps you count on and back.