year 8 maths

3A
Length and perimeter
119
3A Length and perimeter
REVISION
For thousands of years, civilisations have found ways to measure length. The Egyptians, for example,
used the cubit (length of an arm from the elbow to the tip of the middle finger); the Romans used the
pace ( 5 feet); and the English developed their imperial system using inches, feet, yards and miles.
The modern-day system used in Australia (and most other countries) is the metric system, which was
developed in France in the 1790s and is based on the unit called the metre. We use units of length to
describe the distance between two points, or the distance around the outside of a shape, called the
perimeter.
Let’s start: Provide the perimeter
In this diagram some of the lengths are given. Three students
are asked to find the perimeter.
• Will says that you cannot work out some lengths and so the
perimeter cannot be found.
• Sally says that there is enough information and the answer is
9 + 12 = 21 cm .
• Greta says that there is enough information but the answer is
90 + 12 = 102 cm .
Who is correct?
Discuss how each person arrived at their answer.
45 mm
6 cm
■ The common metric units of length include the kilometre ( km) , the metre (m) , the
centimetre (cm) and the millimetre (mm) .
×1000 ×100 ×10
km m cm mm
÷1000 ÷100 ÷10
Key ideas
■ Perimeter is the distance around a closed shape.
• All units must be of the same type when calculating the perimeter.
• Sides with the same type of markings (dashes) are of equal length.
x
y
z
P = 2x + y + z
Cambridge Maths NSW
Stage 4 Year 8 Second edition
ISBN 978-1-108-46627-1 © Palmer et al. 2018
Cambridge University Press
Photocopying is restricted under law and this material must not be transferred to another party.