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• Number lines are straight lines with numbers evenly spaced in order along the line.
• They are usually horizontal, but can have vertical representations too when looking at graphs, thermometers etc.
• Numbers increase when moving right on a number line. Numbers decrease when moving to the left.
• Integers, decimals, and fractions can all be labelled on a number line.

A number line is a representation of a value or a range of values. Number lines provide an ordinal image of a number.

• The divisions on a number line can be any value – eg integers, decimals and fractions.
• Using a number line as a representation enables it to be compared against different numbers.
• Using marked values on a number line can help to calculate or estimate readings on the same scale.
• Number lines can be used to convert between different units – a double number line can be used for this.

Not all numbers on a number line have a value written next to them. It is often necessary to calculate these missing values to read the number line accurately.

There are a few ways to calculate a missing value on a number line. One way is to work out the size of each step on the number line. To do this:

1. Find the difference between the two given values on the number line.
2. Count the number of steps between the two values.
3. Divide the difference by the number of steps.
4. This gives the size of each step. Use this to complete the missing values on the number line.

Sometimes you can find a missing value without calculating each step. For example, it could be quicker to find another value which is halfway between two known points on a number line.

Try practising reading number lines and working out missing values with this quiz. You might need a pen and paper to solve some of these questions.

Number lines are used regularly in everyday life. They are often drawn as horizontal lines, but can also be drawn vertically or curved. Number lines can also be used to convert between different units of measure.

• Number lines such as rulers and tape-measures are used to measure a length or distance from one point to another. Rulers are number lines split into equal increments such as millimetres (mm) and centimetres (cm).

• Thermometers are also a type of number line used to measure temperature, which is a measure of how hot or cold something is. For example, water freezes at 0°C (degrees Celsius) and boils at 100°C

• Scales are often represented as a curved line. They are number lines used to measure weight eg, an amount of produce such as fruit or vegetables, often measured in grams (g) or kilograms (kg).

• Measuring jugs are number lines used to measure the volume of liquids, eg millilitres (ml).