Add, subtract, multiply and divide at the same time (mixed use). You have to buy things first, and you have to add money when you sell them. What you can earn is your bid price minus your purchase price. For example, if you buy a pair of shoes from 20 yuan and sell them to others in 45 yuan, the difference you earn is 45-20=25 yuan. If you sell a pair, you earn 25 yuan. What about the other two pairs? They are 25+. At this time, the multiplication (x) is used. Formula: Quantity X = the money you have been earning * * *. For example, if I sell 20 pairs a day, I get 20x25 yuan, 20 is the number of shoes I sell, and a pair earns 25 yuan (depending on the actual situation, you may not earn 25 for a pair, please refer to the subtraction above). This is only one application of multiplication, and there are many others according to the actual situation.