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Ken Gratton20 Aug 2020
NEWS

How kids can learn from carsales.com.au

Teenagers are being challenged to determine a second-hand car’s value using a spreadsheet program

It’s so simple, yet it’s genius.

AMSI (Australian Mathematical Sciences Institute) has developed a data-based assignment drawing on information freely available through carsales.com.au to whet the interest of secondary school students in years 9 and 10.

The AMSI assignment is titled: ‘Linear Relationships (... and how Maths can help you choose a great car)’.

Which is a much better title than the alternative: ‘How to set up a Bivariate Analysis Spreadsheet in Excel’.

If you’re not familiar with spreadsheet programs – the software world’s hybrid of hammer and magic wand – and don’t realise that Excel is Microsoft’s only true gift to humankind, give up reading right here and now.

There’s a rendered pic of Hyundai’s first ute somewhere else on the site for you to ogle.

But if you do use spreadsheet programs and can follow this, here’s the set-up: Students are asked to enter odometer readings and the asking price of used cars as values in a spreadsheet.

excel spreadsheet 1

The information is easily sourced from carsales, and the goal is to produce a graph of these values in a ‘scatterplot’ format. Adding a trendline to the chart provides a simple means of determining how much you should be paying for a specific car, based on its odometer reading.

Students are asked to filter carsales listings down to a make and model of car from a choice of Suzuki Swift, Mazda2, Toyota Yaris or Hyundai i20 – not the Excel.

After that, students are required to filter the listings to vehicles built between 2000 and 2016 and located in Melbourne. Entering the odometer reading and asking price for five or six of the listings in a ‘bivariate’ range of cells (two columns) in Excel, the students can then create a graph based on the data.

Of course, if you want quality data, you would choose the site that offers the widest range of vehicles for sale in the country, we humbly submit.

Adding the trendline to the chart should reveal what we already know – that asking price falls at roughly the same rate as the odometer reading rises. This is the ‘linear’ relationship between the two sets of data.

odometer day 100 mdfg

In reality, the asking price will naturally be influenced by the car’s condition or its desirability, not just the odometer reading. But as a concept the resource has great potential, now that younger drivers are believed to be more open to buying a car in the post-COVID-19 era.

And we can picture some interesting conversations between parents and their progeny – especially parents of young blokes applying the XLS blowtorch to any number of HSVs, FPVs, WRXs and GTIs.

“No Dad, I’m doing my maths homework...”

Interrogating the data

The assignment doesn’t end with data entry and creating a graph. Students are set a series of tasks, such as the following:

Answer which is the dependent variable (price) and which is the independent variable (kilometres travelled)?

Provide an algebraic equation to express the ‘line of best fit’ (trendline).

wrx sti 005 o5c0

Work out how much the student would expect to pay for a vehicle that has travelled 100,000km.

Explain the linear relationship between kilometres travelled and asking price (in the example provided, it’s a deduction of 5.2 cents for every kilometre travelled).

Determine the constant in the linear equation for line of best fit.

The teaching guide has been provided by AMSI in a downloadable PDF as a resource for teachers, produced with the assistance of teacher Natalie Hammond, of Bayside P-12 College in Melbourne’s inner western suburbs.

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Written byKen Gratton
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