Practical problems of quadratic function in junior high school mathematics A supermarket sells a kind of aquatic product with a sales cost of 40 yuan per kilogram. According to market analysis, if it is sold at 50 yuan per kilogram, 500 kg can be sold in a month, and the monthly sales volume will be reduced by 10 kg for every 1 yuan increase in the sales unit price 1) When the unit price is 55 yuan per kilogram, calculate the monthly sales volume and profit 2) Suppose the unit selling price is x yuan per kilogram and the monthly selling profit is y yuan 3) The store wants to make the monthly sales profit reach 8000 yuan under the condition that the monthly sales cost does not exceed 10000 yuan. How much is the sales unit price?

1. Monthly sales volume = 500-10 * 5 = 450
Monthly sales profit = (55-40) * 450 = 6750 yuan
2.y=(x-40)[500-10(x-50)]
3. Monthly sales = 8000
y= x^2-140x+4800

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