year 8 maths

4I
The Goods and Services Tax (GST)
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Example 27
Calculating the GST
Calculate the GST payable on:
a a table that a manufacturer values at $289
b a bill from a landscape gardener of $2190
SOLUTION
10
a × 289 = 28.9
100
The GST is $28.90 .
10
b × 2190 = 219
100
The GST is $219 .
EXPLANATION
GST is 10% of the value.
Find 10% of $289 .
Find 10% of $2190 .
Example 28
Using the unitary method to find the full amount
A bike has GST of $38 added to its price. What is the price of the bike:
a before the GST? b after the GST?
SOLUTION
a 10% = 38
1% = 3.8
100% = 380
Before the GST was added, the cost of the
bike was $380 .
b After the GST, the price is $418 .
EXPLANATION
Divide by 10 to find the value of 1% .
Multiply by 100 to find 100% .
Add the GST to the pre-GST price.
$380 + $38 = $418
Example 29
Using the unitary method to find the pre-GST price
The final price at a café, including the 10% GST, is $137.50 . What is the pre-GST price of the meal?
SOLUTION
110% = 137.50
1% = 1.25
100% = 125
The pre-GST cost is $125 .
Alternative method:
$137.50 ÷ 1.1 = $125
EXPLANATION
The GST adds 10% to the cost of the meal.
100% + 10% = 110%
∴ Final price is 110% .
Divide by 110 to find the value of 1% .
Multiply by 100 to find 100% .
Dividing by 1.1 gives the original price, excluding GST.
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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