year 8 maths

5E
Introducing rates
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Example 12
Writing simplified rates
Express each of the following as a simplified rate.
a 12 students for two teachers b $28 for 4 kilograms
SOLUTION
EXPLANATION
a 6 students/teacher 12 students for 2 teachers
÷2 ÷2
6 students for 1 teacher
b $7/kg
$28 for 4 kg
÷4 ÷4
$7 for 1 kg
Example 13
Finding average rates
Tom was 120 cm tall when he turned 10 years old. He was 185 cm tall when he turned 20 years old.
Find Tom’s average rate of growth per year between 10 and 20 years of age.
SOLUTION
65 cm in 10 years
÷10 ÷10
6.5 cm in 1 year
Average rate of growth = 6.5 cm/year
EXPLANATION
Growth = 185 − 120 = 65 cm
Divide both numbers by 10 .
Exercise 5E
UNDERSTANDING AND FLUENCY
1–3, 4 3, 4(½), 5
4–5(½)
1 Which of the following are examples of rates?
5
A $5.50 B 180 mL/min C $60/h D
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E 4.2 runs/over F 0.6 g/L G 200 cm 2 H 84c/L
2 Match each rate in the first column with its most likely rate in the second column.
e mployee’s wage
90 people/day
speed of a car $2100/m 2
cost of building a new home 68 km/h
population growth
64 beats/min
resting heart rate
$15/h
3 Write typical units for each of the following rates.
a price of sausages b petrol costs
c typing speed d goal conversion rate
e energy nutrition information f water usage in the shower
g pain relief medication
h c ricket team’s run rate
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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