Supplementary questions. The relationship between your unit price and sales volume is unknown.

Solution: We raise the price by X yuan.

Profit = pure profit × sales volume

So the equation y = (40+x) (400-20x) =16000+320x-20x? =-20(x-8)？ + 14720

When x=8, the minimum value of the equation is 14720.

Therefore, the sales price should be increased in 8 yuan. At this time, the price of each piece is 108 yuan. Maximum profit for half a month 14720 yuan.

For that silence ~