According to the previous statistical data, if the retail price is set at 4 yuan per bottle, 400 bottles can be sold every month; if the retail price is reduced by 0.05 yuan, 40 bottles can be sold more. & nbsp; therefore, please design a plan for the store: how much yuan should the selling price be set and how many bottles of this kind of beverage can be purchased every month to get the maximum profit?

According to the previous statistical data, if the retail price is set at 4 yuan per bottle, 400 bottles can be sold every month; if the retail price is reduced by 0.05 yuan, 40 bottles can be sold more. & nbsp; therefore, please design a plan for the store: how much yuan should the selling price be set and how many bottles of this kind of beverage can be purchased every month to get the maximum profit?

Suppose the selling price is x yuan / bottle, then we know that the sales volume of the current month is 4 − x0.05 × 40 + 400 = 400 (9 − 2x) (bottle) (3 points), so the profit of the current month is f (x) = 400 (9-2x) (x-3) = 400 (- 2x2 + 15x-27) (yuan) (6 points)