A shopping mall in Shenzhen bought a batch of Hainan watermelons before the Spring Festival. They can sell 500 kg a day and make a profit of 0.3 yuan per kg. In order to reduce the inventory as soon as possible, the shopping mall decided to take appropriate price reduction measures. The survey shows that when the sales price is reduced by 0.1 yuan, the sales volume will be increased by 100 kg per day. If the shopping mall wants to make an average profit of 120 yuan per day, how much should the price be reduced per kg of watermelons?

A shopping mall in Shenzhen bought a batch of Hainan watermelons before the Spring Festival. They can sell 500 kg a day and make a profit of 0.3 yuan per kg. In order to reduce the inventory as soon as possible, the shopping mall decided to take appropriate price reduction measures. The survey shows that when the sales price is reduced by 0.1 yuan, the sales volume will be increased by 100 kg per day. If the shopping mall wants to make an average profit of 120 yuan per day, how much should the price be reduced per kg of watermelons?

Suppose that the price of watermelons per kilogram should be reduced by X Yuan, and the current profit is (0.3-x) yuan, then the market will sell more than 100x0.1 = 1000xkg. (0.3-x) (500 + 1000x) = 120150-200x-1000x2 = 1201000x2 + 200x-30 = 0100x2 + 20x-3 = 0, (10x + 3) (10x-1) = 0, and the solution is X1 = - 0.3 (the price reduction cannot be negative, which is not satisfactory), X2 = 0.1. Answer: the price of watermelons per kilogram should be reduced by 0.1 yuan