题目

某商店购进一批单价为20元的日用品,如果以单价30元销售,那么半个月内可以售出400件.根据销售经验,提高单价会导致销售量的减少,即销售单价每提高1元,销售量相应减少20件.售价提高多少元时,才能在半个月内获得最大利润? 最大利润是多少？ 答案：设提高x元，销售利润为y元． 根据题意，得y=（10+x）（400-20x）=-20x2+200x+4000， 当x=-200/2×(-20)=5时，y最大=4500，所以，销售单价提高5元，才能在半月内获得最大利润4500元． 短文改错 此题要求改正所给短文中的错误。对标有题号的每一行作出判断：如无错误，在该行右边横线上画一个勾(√)；如有错误(每行只有一个错误)，则按下列情况改正： 该行多一个词：把多余的词用斜线(＼)划掉，在该行右边横线上写出该词，并也用斜线划掉。 该行缺一个词：在缺词处加一个漏字符号(∧)，在该行右边横线上写出该加的词。 该行错一个词：在错的词下画一横线，在该行右边横线上写出改正后的词。 注意：原行没有错的不要改。 My cousin Xiao Hong and I went on trip to my uncle’s 1．________ last Sunday．We were riding along a hillside then suddenly 2．________ some big stones were rolled down and knocked us off our bikes． 3．________ Xiao Hong’s legs got seriously hurt and so was mine．We 4．________ couldn’t move a little．Fortunately, I saw some farmers ahead． 5．________ Waving our hands, we cried for help like crazy．On hearing 6．________ us, they ran to the spot as fast as they can．Thanks to 7．________ their help, we were all sent to a nearby hospital and received 8．________ medical treatment in time．Although we do not know about their 9．________ names, we feel they like our dear big brothers and sisters． 10．________