It is a very important task for students to experience the practical value of mathematics and its role in solving practical problems. Living in a commodity economy society, it is very necessary for students to master the necessary knowledge of commodity sales in order to engage in current and future production and life.

In order to meet this demand, in recent years, the problem of commodity sales in mathematics teaching has become an important theme, which has penetrated into many mathematical fields such as equations, functions and inequalities. To solve this kind of problem, students should not only be familiar with the related concepts of commodity sales, but also be able to use known mathematical knowledge to build mathematical models.

Due to the lack of life experience and social practice in this field, students often have no way to deal with such problems, which has become a difficult point for junior high school students to learn mathematics.

Firstly, several important concepts and formulas are clarified.

(1) The purchase price of a commodity refers to the price when the store buys the commodity (also called the purchase price).

(2) The clearly marked price of goods refers to the price marked by the label when the store sells the goods, sometimes called pricing (which can be discounted).

(3) The selling price of goods refers to the transaction price between the buyer and the seller when the store sells goods.

(4) Discount refers to the percentage of the store's selling price in the list price when selling goods. Generally, 10% is 10% off.

(5) Commodity profit (profit) = commodity price-commodity purchase price.

(6) The marked price (pricing) of the commodity = the purchase price of the commodity+profit+discount price.

(7) The selling price (selling price) of the commodity = the marked price of the commodity x the selling discount of the commodity.

Second, be familiar with the solutions to typical problems

For example? (20 14 Liaocheng Senior High School Entrance Examination) A clothing store bought two new clothes A and B for 6000 yuan. After selling them at the marked price, it can get a gross profit of 3800 yuan (gross profit = selling price-buying price). The purchase price and list price of these two clothes are shown in the table:

(1) The number of pieces purchased for each of these two kinds of garments; (2) If A's clothes are sold at 20% off the list price and B's clothes are sold at 30% off the list price, how much money will the clothing store earn less than the clothes sold at the list price after all these clothes are sold out?

Analysis: (1) Assuming that A kind of clothing buys X pieces and B kind of clothing buys Y pieces, the equations are established from total price = unit price × quantity and profit = selling price-buying price to find its solution. (2) Calculate the discount price separately, and then solve it according to the total profit = the profit of clothes in A+the profit of clothes in B. ..