year 8 maths

Chapter summary
331
Average rates
720 km driven in 10 hours
Average speed = 720
10
= 72 km/h
Simplified rates
• 25 km/h many km per one hour?
• $12/kg many $ per one kg?
Distance
Distance–time graph
Rates
Comparing
two quantities with
different units
Time
• Steeper lines show greater
speed than less steep lines.
• Flat segment means the object
is at rest.
Reading the graph:
• Start on given distance. Move
across to line, then down to time
scale (or in reverse).
s : speed
d : distance
t : time
d
s t
d
s t
d
s
t
s =
d
t
d = s × t
d
t =
s
Unitary method to change units
1
For an 18 km jog in 1
2
hours
determine average rate in m/min.
1
1 18 km in 1 2 hours 1
÷1
÷1
2 18
2
km in 1 hour
1 1 2
÷60
12 000 m in 60 min
200 m in 1 min
÷60
Average speed = 200 m/min
1 part
1 part
Unitary method with rates
4 L paint to cover 80 m 2
? L to cover 165 m 2
4 L for 80 m
÷80
2 ÷80
4
L for 1 m 2
×165 4 80
×165
× 165 for 165 m2
80
1 part
8.25 L for 165 m 2
Cambridge Maths NSW
Stage 4 Year 8 Second edition
ISBN 978-1-108-46627-1 © Palmer et al. 2018
Cambridge University Press
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