2022英语周报新目标第56期答案

18.解:(1)由已知得10×(0.010 0.015 0.015 m 0.025 0.005)=1,所以m=0.030(2分)(2)平均数x=45×0.1 55×0.15 65×0.15 75×0.3 85×0.25 95×0.05=71设中位数为n,则0.1 0.15 0.15 (n-70)×0.03=0.5,所以n==3≈73.33故可以估计该企业所生产口罩的质量指标值的平均数为71,中位数为73.33.(6分)(3)由频率分布直方图可知,质检人员所抽取的100个口罩中,一等品、二等品的个数分别为60,40所以由分层抽样的方法可知,从该企业所抽取的100个口罩中,抽出5个口罩,抽出一等品、二等品的个数分别为3,2,记这3个一等品分别为a,b,c,记这2个二等品分别为d,e,则从这5个口罩中抽取2个的所有可能结果为(a,b),(a,c),(a,d),(a,e),(b,c)(b,d),(b,e),(c,d),(c,e),(d,e),共10个,其中恰有1个口罩为一等品的结果有(a,d),(a,e),(b,d),(b,e),(c,d),(c,e),共6个故这2个口罩中恰好有1个口罩为一等品的概率P(12分

第二节One possible versionDear mr. smithIm writing to ask for a three-day leave, for I can'Iattend your English classes from Monday to Wednesday nexOwing to a severe headache, I have made an appoint-ment with a specialist. and my mother will take me to seehim. It's a great pity that I will miss your interesting lessons but I hope you will excuse my absence. I promise tomake up for the missed lessons after I return to school.Your kind permission will be greatly appreciatedYeLi Hua

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