How to calculate a discount
To find the amount saved, multiply the original price by the discount percentage and divide by 100. Subtract that from the original price to get the final sale price. For example, 25% off $80 saves $20, so you pay $60.
Stacking discounts
When a store offers "an extra 10% off" an already-reduced price, the second discount applies to the lower price, not the original so two 20% discounts are not the same as 40% off.