Percentages and GST

SubjectMathematics YearYear 8 CurriculumAC v8.4 Time170

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This set of resources provides opportunities for students to solve problems involving percentages, rates and proportions using technology (spreadsheets) in the context of the goods and services tax GST). 

Australian Curriculum or Syllabus

Achievement standard

By the end of Year 8, students solve everyday problems involving rates, ratios and percentages. They describe index laws and apply them to whole numbers. They describe rational and irrational numbers. Students solve problems involving profit and loss. They make connections between expanding and factorising algebraic expressions. Students solve problems relating to the volume of prisms. They make sense of time duration in real applications. They identify conditions for the congruence of triangles and deduce the properties of quadrilaterals. Students model authentic situations with two-way tables and Venn diagrams. They choose appropriate language to describe events and experiments. They explain issues related to the collection of data and the effect of outliers on means and medians in that data.

Students use efficient mental and written strategies to carry out the four operations with integers. They simplify a variety of algebraic expressions. They solve linear equations and graph linear relationships on the Cartesian plane. Students convert between units of measurement for area and volume. They perform calculations to determine perimeter and area of parallelograms, rhombuses and kites. They name the features of circles and calculate the areas and circumferences of circles. Students determine the probabilities of complementary events and calculate the sum of probabilities.

Content descriptions

Carry out the four operations with rational numbers and integers, using efficient mental and written strategies and appropriate digital technologies (ACMNA183).

Solve problems involving the use of percentages, including percentage increases and decreases, with and without digital technologies (ACMNA187).

Solve a range of problems involving rates and ratios, with and without digital technologies (ACMNA188).

Solve problems involving profit and loss, with and without digital technologies (ACMNA189).

Teacher resources

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Goods and services tax (GST)


Using spreadsheets

Student learning resources

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What is GST?


Sales, GST and profit


Impact of GST

Suggested activity sequence

This sequence is intended as a framework to be modified and adapted by teachers to suit the needs of a class group. If you assign this activity to a class, your students will be assigned all student resources on their 'My learning' page. You can also hand-pick the resources students are assigned by selecting individual resources when you add a work item to a class in 'My classes'.

Part A: What is GST?

  1. Begin by playing the Goods and services tax (GST) video to give students an overview of GST.
  2. Discuss how GST works for businesses that collect GST, including how they can get credits for the GST they paid on goods and services.

GST collected - GST credits = Amount owed to the ATO.

Part B: Calculating GST

  1. Explicitly teach students how to calculate GST from both the GST exclusive price and the GST inclusive price (that is, working forwards and backwards). Calculating GST at 10 percent – How-to-sheet might be a helpful resource for students.
  2. You might like to get students to complete a table like this one as a practice activity:

    Price (excluding GST)


    Price (including GST)































  3. Students complete part 1 of the worksheet.

Part C: Investigating GST, profit and profit margins

  1. As a class, read through part 2 of the worksheet. If necessary, use examples to demonstrate how to calculate profit, profit margins and percentage increase and decrease.
  2. Display and explain how to use spreadsheets using the visualiser.
  3. Reinforce learning by modelling the process of setting up an excel spreadsheet using the following scenario. If you’re all working together on this, everyone will need access to a computer with spreadsheet software.
    1. You work in an outdoor store and one of your tasks is to price items. The store wants to sell its down jackets for $118, beanies for $11, hiking shoes for $145 and backpacks for $46. How much GST do they need to add to each one and what will the final price on the price tag be?

    It might be useful for students to have a copy of Making an Excel spreadsheet using GST as an example – How-to-sheet before you start so they can follow along.

  4. Students complete part 2 of the worksheet.
  5. Walk students through the investigation instructions, reminding them of the similarities to the problem you modelled.
  6. Students complete the investigation. Students may benefit from working individually and/or in small discussion groups.
  7. As a class, discuss students’ findings.