Shopping math is a practical skill that helps you calculate costs, discounts, taxes, and savings while making purchases. Here's a quick guide to the key concepts and formulas you need:
To figure out how much you’ll save with a discount:
Formula:
Discount Amount = Original Price × (Discount % ÷ 100)
Final Price = Original Price - Discount Amount
Example:
A $50 item with a 20% discount:
- Discount Amount = $50 × (20 ÷ 100) = $10
- Final Price = $50 - $10 = $40
To include sales tax in your total:
Formula:
Sales Tax Amount = Price × (Tax % ÷ 100)
Total Price = Price + Sales Tax Amount
Example:
A $100 item with a 7% tax:
- Sales Tax Amount = $100 × (7 ÷ 100) = $7
- Total Price = $100 + $7 = $107
If you have a discount and sales tax:
1. Calculate the discounted price first.
2. Then, calculate the sales tax on the discounted price.
Example:
A $200 item with a 15% discount and 8% tax:
- Discounted Price = $200 × (1 - 0.15) = $170
- Tax = $170 × 0.08 = $13.60
- Final Price = $170 + $13.60 = $183.60
To compare prices between products:
Formula:
Unit Price = Total Price ÷ Quantity
Example:
- A 12-pack of soda costs $6.
Unit Price = $6 ÷ 12 = $0.50 per can.
- Compare this to a 6-pack for $4.
Unit Price = $4 ÷ 6 = $0.67 per can.
- The 12-pack is cheaper per unit.
When you’re shopping with a budget:
- Set a Total Limit (e.g., $100).
- Subtract each item’s price as you shop.
- Keep a running total to ensure you stay within your budget.
Example:
Budget = $50
- Item 1: $15 Remaining = $50 - $15 = $35
- Item 2: $20 Remaining = $35 - $20 = $15
- Item 3: $18 Over Budget!
To calculate how much an item's price changes:
Formula:
% Change = [(New Price - Old Price) ÷ Old Price] × 100
Example:
An item goes from $40 to $50:
- % Change = [(50 - 40) ÷ 40] × 100 = 25% increase
Pro Tip: Keep a calculator or a shopping app handy for quick calculations!