Discounts and Sales Tax
Apply percent decrease or increase to price.
Key idea
Apply percent decrease or increase to price.
In depth
A discount of d% means you pay (100−d)% of the price: multiply by (1 − d/100). Sales tax of t% adds: multiply by (1 + t/100). Apply them in sequence on the changing price.
Worked example
A 30 shirt with 20% off costs 30 × 0.8 = 24. Add 10% tax: 24 × 1.1 = 26.40.
Formula
Real-world uses
- Working out the final price after a 20% off sale and a tax
- Checking receipts and budgets
Common mistake
Treating a discount followed by tax as cancelling out. The percentages apply to different amounts.
How to learn this
- Read the key idea and say it in your own words.
- Work through the worked example, then try a similar problem.
- Use the interactive lesson’s visual and mini-quiz to check the pattern.
Frequently asked questions
What is Discounts and Sales Tax?
Apply percent decrease or increase to price. It is a topic at the intermediate level in Arithmetic & Number Sense.
What is the formula for Discounts and Sales Tax?
The key formula is price × (1 − d).
Where is Discounts and Sales Tax used in real life?
Real-world examples: Working out the final price after a 20% off sale and a tax; Checking receipts and budgets.
What should I learn before Discounts and Sales Tax?
Make sure you are comfortable with Percentage Change, the previous topic in Arithmetic & Number Sense.
What is a common mistake with Discounts and Sales Tax?
Treating a discount followed by tax as cancelling out. The percentages apply to different amounts.
How can I practise Discounts and Sales Tax?
Open the interactive lesson, play with the visual, then answer the three-question mini-quiz. Getting two right marks the topic complete.
What comes after Discounts and Sales Tax?
Move on to Simple Interest next.
Related intermediate topics in Arithmetic & Number Sense
- Long Multiplication – Multiply by each digit of the multiplier, shift by place value, then add partial products.
- Long Division – Divide, multiply, subtract and bring down repeatedly to get the quotient.
- Factors and Multiples – Factors divide a number exactly; multiples are its products with whole numbers.
- Divisibility Rules – Quick tests: by 2 last digit even, by 3 digit-sum divisible by 3, by 5 ends 0/5, by 9 digit-sum divisible by 9.
- Prime Numbers – A prime has exactly two positive divisors: 1 and itself.
- Composite Numbers – Numbers greater than 1 with more than two factors.