year 8 maths

304 Chapter 5 Ratios and rates
Example 16
Solving rate problems using the unitary method
A truck uses 4 L of petrol to travel 36 km. How far will it travel if it uses 70 L of petrol?
SOLUTION
Rate of petrol consumption
36 km for 4 L
÷4 ÷4
9 km for 1 L
×70 ×70
630 km for 70 L
Truck will travel 630 km on 70 L .
EXPLANATION
Find the petrol consumption rate of 1 unit by
dividing both quantities by 4 .
Solve the problem by multiplying both quantities
by 70 .
Example 17
Converting units using the unitary method
Melissa works at the local supermarket and earns $57.60 for a 4 -hour shift.
How much does she earn in c/min?
SOLUTION
Wage = $57.60 for 4 hours
÷4
$14.40 for 1 hour
÷4
1440c mL for 60 minutes
÷60 ÷60
24c for 1 minute
Melissa earns 24c /min.
EXPLANATION
Write down Melissa’s wage rate.
Find the rate of $ per 1 hour.
Convert $ to cents, and hours to minutes.
Divide rate by 60 to find rate of cents per minute.
Exercise 5F
UNDERSTANDING AND FLUENCY
1–6, 8 4–7, 8(½)
5–6(½), 7, 8(½)
Example 14
1 If 8 kg of chicken fillets cost $72 , how much would 3 kg of chicken fillets cost?
2 If one dozen tennis balls cost $9.60 , how much would 22 tennis balls cost?
3 If three pairs of socks cost $12.99 , how much would 10 pairs of socks cost?
4 If 500 g of mince meat costs $5.50 , how much would 4 kg of mince meat cost?
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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