Number And Algebra - Chapter 7 Applying Ratios And Rates - Nelson Think Math Page 20
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32N E L S O N T H I N K M A T H S
8
A u s t r a l i a n C u r r i c u l u m
for the
7.3
Practical rates and ratios
Puzzle sheet
The word scale has many meanings. Earlier in this chapter, scale was used to refer to the markings
Scale enlargement
on a measuring device. A scale drawing of an object is a copy that has the same shape and
MAT08NAPS00026
proportions as the real object. A scale drawing is similar to the outline of the object, so it is an
enlargement or reduction. The length on the drawing is divided by the corresponding real length to
1
obtain the scale. A scale of
is usually written as 1 : 1000.
1000
Scale drawings are used by builders, designers, artists,
scientists and engineers.
Here is a photo of an ant.
The head and body of the real ant is 4 mm long.
In the photo, the ant is 40 mm long.
photo length
Scale ¼
real length
¼ 40 mm 4 4 mm
¼ 10 : 1
This means that the scale factor is 10. Therefore 10 mm
on the drawing represents 1 mm on the actual object.
This photo is an enlargement of the actual size.
Here is a scale drawing of a plane.
The real plane is 70 m long.
In the drawing the plane is 70 mm long.
70 m
drawing length
Scale ¼
real length
70 mm
¼
70 m
70 mm
¼
70 000 m
1
¼
1000
¼ 1 : 1000
1
This means that the scale factor is
.
1000
Therefore 1 mm on the drawing represents 1000 mm (1 m) on the actual object.
This scale drawing is a reduction of the actual size.
Important!
Scales
The standard way of writing a scale is:
Length in drawing : Length in real object
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