18.【解析】(1)根据已知数据可得如下列联表:级品非一级品总计粗玉米面20100细玉米面70100总计150200(2分)K2=20×(20×7030×802=2679202,参照临界值表可知,有85%的把握认为产品是否为一级品与玉米面粗细有关(4分)(2)生产一袋粗玉米面的平均利润约为10×20+60×5-2×204.6(元)生产一袋细玉米面的平均利润约为10×30+5×40-2×30=4.4(元).(6分)100(3)从一级品中按分层抽样的方法抽取10袋则其中粗玉米面4袋,细玉米面6袋,从这10袋中随机选出2袋定为特级品,则粗玉米面被选出的袋数x的可能取值为0,1,2,则P(X=3cl ck 8P(X=1)=CACe(9分)则X的分布列为0282315所以E(x)=0×-+1×+2242分

第二节书面表达Dear Mr. Johnson.I'm Li Hua, a student of Student EnglishAssociation. I'm writing to invite you to be a judge atour English speech contest to be held in our schoollecture hall on June IstThe English contest will start at 2: 00 pm and lastfor about three hours. Ten students who get thechance to give speech are chosen from differentclasses. They will deliver their speeches on the giventopic"Man and Nature". We hope you will acceptour invitation if it is convenient for you. Please came at 44876655, if you have any questions.I am looking forward to your replYoursLi Hua

以上就是英语周报七年级下册2019～2022第58期答案，更多英语周报答案请关注本网站。

本文地址： http://www.ncneedu.cn/post/18462.html

文章来源：admin

版权声明：除非特别标注，否则均为本站原创文章，转载时请以链接形式注明文章出处。