Discount formula
Sale price = original price × (1 − discount % ÷ 100)
An 80.00 item at 25% off costs 80 × 0.75 = 60.00, a saving of 20.00.
Stacked discounts do not add up
When a second discount applies, it is taken from the already reduced price. 25% off followed by an extra 10% off is 0.75 × 0.90 = 0.675 of the original price, an effective discount of 32.5%, not 35%.
Finding the original price
If you know the sale price and the discount, divide the sale price by (1 − discount ÷ 100). An item that costs 60 after 25% off was originally 60 ÷ 0.75 = 80.