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There are 100 centimetres in a metre.

\(214 \div 100 = 2.14 \text{m}\)

There are 10 millimetres in a centimetre.

\(214 \times 10 = 2140 \text{mm}\)

It is not always easy to decide whether to divide or multiply by the conversion factor.

Metres are larger than centimetres so the number of centimetres will be more than the number of metres. Divide the number of centimetres by the conversion factor.

Millimetres are smaller than centimetres so the number of millimetres will be more than the number of centimetres. Multiply the number of centimetres by the conversion factor.

Check the answer - should it be smaller or larger than the original number?

Metric units are most often used today, however in some cases imperial units are still used and so it is important to be able to convert between them.

The imperial system uses the following units:

• length in inches and miles
• mass in pounds (lb), ounces (oz) and stones
• volume in pints and gallons

The following conversions are commonly tests on the M5 paper and it is necessary to know the conversions.

The sign \(\approx\) means approximately equal to.

MEMORISE THESE CONVERSIONS

All of the conversions in the table above have been written with the 1 on the left side of the rule.

• When units are being converted from the unit of the left to the unit on the right, multiply by the conversion.
• When units are being converted from the unit on the right to the unit on the left, then divide by the conversion.

Example

A marathon is 26 miles. How far is this in kilometres?

Solution

Using the conversion:

\( 1 \text{mile} \approx 1.6 \text{km}\)

\( \rightarrow \rightarrow \rightarrow\)

Left to right, MULTIPLY by conversion

\(26 \text{miles} = 26 \times 1.6 = 41.6 \text{km}\)

Example

Poppy has a 10kg maximum baggage allowance on a flight. She weighed her bag on scales at her home and it was 18 lbs.

Will she be allowed to take this bag on the flight?

Solution

Using the conversion:

\( 1 \text{kg} \approx 2.2 \text{lbs}\)

\( \leftarrow \leftarrow \leftarrow\)

Right to left, DIVIDE by conversion

\(18 \text{lbs} = 20 \div 2.2 = 8.18 \text{kg}\)

She can take her bag on the flight, as \(8.18 \text{kg} < 10 \text{kg}\).