题目

Emily has a pen friend in England．Her name is Alice．They write to each other twice a month．In her last letter Alice told Emily how she spent a week in Japan with her family．Here is Emily's reply （答复）．Dear Alice，Thank you for your last letter．I enjoyed reading it very much．It seemed that you had a more wonderful summer vacation than I did．I hope I can also go to Japan one day．In this letter I will tell you about my best friend．Her name is Kate．Kate has long brown hair and blue eyes．We are both 13years old，but she is a little taller than me．She is always hap某商场购进一种单价为40元的篮球，如果以单价50元售出，那么每月可售出500个，根据销售经验，销售单价每提高1元，销售量相应减少10个1.设销售单价提高x元(x为正整数)，写出每月销售量y（个）与x（元）之间的函数关系式；2.假设这种篮球每月的销售利润为w元，试写出w与x之间的函数关系式，并通过配方讨论，当销售单价定为多少元时，每月销售这种篮球的利润最大，最大利润为多少元？