- How do you find the original price before a discount?
- Divide the sale price by (1 - discount percentage as decimal). For example, if an item costs $70 after a 30% discount, divide 70 by (1 - 0.30) = 70 / 0.70 = $100 original price.
- Why cannot you just add the discount percentage back to the sale price?
- Because the original discount was calculated as a percentage of the higher original price, not the lower discounted price. Adding 30% to $70 gives $91, which is incorrect ($100 was the original).
- How do you calculate the pre-tax price from a total with sales tax or VAT?
- Divide the total receipt amount by (1 + tax rate as decimal). If a laptop costs $1,100 including 10% tax, the pre-tax price is 1,100 / 1.10 = $1,000.