英语周报八年级下册黔南2020―2021贵阳答案

第二节书面表达One possible version:Dear classmates,While watching the historic moment when the threeChinese astronauts were sent up into space,I felt so excitedthat I couldn't hold back my tears.This great achievementhas showed not only our advanced technology but also thegreat power of China.At the same time,it made me realizeour responsibility.And I have made up my mind to have agood command of knowledge.Only in this way can we makegreat contributions to our country Dear classmates,let'sstudy harder for a more powerful China!Thanks for your listening.

20.(12分)解：(1)平均成绩为：10×(45×0.005+55×0.02+65×0.025+75×0.03+85×0.015+95×0.005)=69.5.…4分区间[80,100]内的概率为10×(0.015+0.005)=三，故成续落在区间[70,10]内的概率为10x003+0015+0.05)=7故Y~B2,分00+E0=2x2*写号由题意，Z可能的取值为0,1,2,3,4，且X≤Y.rZ=0=x=0y=0=0-r-mz-W=x=r==G90--高PZ-2)-P0.PPz==Px=y=2)=G写3房3P2=4=PX=2y=2)=(}=25E(Z)=0x+lx34x0+2×00+3×3+3×*4>255故有E(X)+E(Y)=E(Z).…12分

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