Developing Critical Numeracy Across the Curriculum

Teaching Activity

Costs Soaring

How can payment systems for resources encourage us to live more sustainably?
9/10 Stage: 11/12
with emphasis on:

Maths Concepts: Number, graphing
Context: Environment, Society
Critical Numeracy: De-coding, Meaning-making,
Using, Analysing
Date of Article: 04/06/09, pg 1
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Student Worksheet
Student worksheet answers

Teacher Guidelines:

This article looks at the percentage increase in power bills as Aurora moves from a tiered payment scheme to a flat rate scheme. In the tiered scheme the more electricity you use the cheaper the tariff rate becomes. Is a tiered scheme appropriate for encouraging sustainable use of electricity? How does such a scheme work and what are the benefits of moving to another model? This article gives an opportunity to explore how pricing structures can be used to encourage people to change their consumption.

Aurora has tips for reducing electricity usage in the home at

Orienting Questions

How can payment systems for resources encourage us to live more sustainably?

What are the true costs of providing a service for electricity? Does cost come down the more you use? Should cost savings be shared with the user? What is the impact of costs on the user?

De-coding and Meaning-making

The worksheet helps the students work out from the article what a tiered payment system for electricity usage means. They calculate the costs that the user would pay under the old and new systems and the percentage increase. They use these data to plot a graph so that they can easily compare the change for different households. Students could be encouraged to bring in their electricity bills with the Tariff 31 amount of kWh so that they can use their graph to work out their likely increase in charges.

Using and analysing

The worksheet asks students to consider the advantages and disadvantages of a tiered payment system and to come up with their own that would encourage sustainable use of electricity.

Classroom discussion could consider other tiered systems (like the income tax system) and why these are devised. Students could discuss whether they think the price rises under a new system are significant and what the impact on users might be. Has the article deliberately made the increases seem worse than they likely will be to incite responses? What might be the different views of stakeholders - the electricity providers, the households/users, environmentalists. Which view was the article promoting?


What did you learn? How has your thinking on this topic changed? What new maths skills have you developed? What thinking strategies have you found useful?

What investigation would you like to consider now?


Students might be interested in doing an energy audit of their home, class or school. Aurora provides worksheets to help calculate kWh usage and cost per appliance.

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