Counting the product, calculating the discounted price on the products and the total amount of money you spend on the shopping.
Discounts and when you're done buying something, you check your receipt if the clerk gave you the right amount of money
Percentages (ex. If a one hundred dollar blender is 50% off, then it will cost $50) and money exchange (ex. If you pay for the $50 blender with a$100 bill then your change is $50).