How to teach rational-number and money word problems
Year 7 (ages 12 to 13)
This unit applies fraction, decimal and percentage skills to real money problems: discounts, spending a fraction of an amount, and adding tax (GST), each solved by the same two-step pattern of calculate-then-adjust.
How to teach it
- Teach the common two-step pattern: calculate the relevant amount (discount, spent, tax), then add or subtract it from the original.
- Work through a discount problem step by step: discount amount first, then sale price.
- Extend to GST/tax problems, noticing the pattern is the same but adding instead of subtracting.
- Cover 'spend a fraction, find what's left' problems, reinforcing that the fraction spent and the fraction remaining add to 1.
- Use realistic prices and rates (10% GST, common discount percentages) so the context stays believable.
Worked example
A jacket costs $80. It is on sale for 25% off. What is the sale price? Discount = 80 x 25/100 = $20 Sale price = $80 - $20 = $60
Common mistakes
- Adding the discount instead of subtracting it (or vice versa for tax).
- Calculating the percentage of the wrong amount (e.g. the sale price instead of the original price).
- Forgetting a final step, e.g. stopping at the discount amount instead of the actual sale price.
- Mixing up 'the fraction spent' with 'the fraction remaining' in a spending problem.
Frequently asked questions
How do you find a sale price after a percentage discount?
Calculate the discount amount (price x discount percentage), then subtract it from the original price. A $80 item at 25% off: discount = $20, sale price = $60.
How do you find the total price including tax (GST)?
Calculate the tax amount (price x tax rate), then add it to the original price. A $50 item with 10% GST: tax = $5, total = $55.
How do you find how much money is left after spending a fraction of it?
Calculate the fraction of the total spent, then subtract it from the total. Spending 1/4 of $80 leaves $80 - $20 = $60.
What year are rational-number and money word problems taught?
In the Australian Curriculum this is a Year 7 skill (AC9M7N09): using mathematical modelling for practical problems with rational numbers and percentages, including money.
Practise with free worksheets
Printable worksheets with answer keys that are never wrong.