Percentage Change and Discount
Percentage change measures how much a quantity has increased or decreased relative to its original value. Discount is a common real-world application where a percentage reduction is applied to a price.
What You Need to Know
Key Concept Diagram
Percentage increase: ((new - original) / original) x 100%
Percentage decrease: ((original - new) / original) x 100%
To find a percentage of an amount: divide the percentage by 100 and multiply by the amount
Discount = discount percentage x original price / 100
Sale price = original price - discount; or sale price = (100 - discount%) / 100 x original price
Key Vocabulary
Percentage Change
The increase or decrease in a value expressed as a percentage of the original value
Discount
A reduction in price, usually expressed as a percentage of the original price
Markup
An increase in price, expressed as a percentage of the cost price
GST
Goods and Services Tax: a 10% tax added to most goods and services in Australia
Knowledge Check
Select the correct answer for each question. Click "Check Answer" to see if you are right.
Question 1
A jacket costs $80 and is on sale at 25% off. What is the sale price?
Question 2
A phone's price increased from $400 to $480. What is the percentage increase?
Question 3
A pair of shoes originally costs $120. After GST (10%) is added, what is the total price?
Key Concepts Summary
- ●Percentage increase: ((new - original) / original) x 100%
- ●Percentage decrease: ((original - new) / original) x 100%
- ●To find a percentage of an amount: divide the percentage by 100 and multiply by the amount
- ●Discount = discount percentage x original price / 100
- ●Sale price = original price - discount; or sale price = (100 - discount%) / 100 x original price