2022英语周报七年级上册第12期答案

第二节One possible versionWhen Norah heard of her mothers plan, she was terhappy. She couldnt wait to see Dan at once. Hardly hadthey met Dan in his yard when Norah shouted excitedlyShe ran right up to him as if she had known him all of herlife and she was climbing all over him like a monkeyAnd of course every time I turned around. she d comeback over and hug me again, " Dan said. When it was timeto leave, Norah and her mom passed the rose bush by thedoor. Dan picked a big red rose and gave it to Norah, saying, "This is a symbol of our friendship.The mother and her daughter hane been visiting himceely, erer since. Every time they went there, the old andthe young would play games and tell each other secretsorah considers Dan as a family member and Dan has neverbeen alone again. "Norah helped me recover from my sad-ness and gave me something to live for, Dan said, with afresh shave and haircut

19.(理科)【解析】(1)设事件D为:引种三种树苗,至少自然成活2棵则P(D)=0.8×0.75×0.25×2+0.2×0.75×0.75+0.8×0.75×0.75=0.8625(2)X的可能取值为100,150,300,350则有:P(X=100)=(1-0.75)×0.2=0.05,P(X=150)=(1-0.75)x0.8×0.2=0.04,P(X=300)=0.75,P(X=350)=(1-0.75)×0.8×0.8=0.16所以其分布列如下X100300350P0.050.040.750.16E(X)=100×0.05+150×0.04+300×0.75+350×0.16=292(文科)【解析】(1)由题意可得0.02+0.1+a+0.35+0.2+0.1+0.03=1,解得a=0.2(2)设事件A为遇到红灯的个数为4,事件B为遇到红灯的个数为5事件C为遇到红灯的个数为6个及6个以上,则事件“至少遇到4个红灯”为A∪BUC,因为事件A,B,C互斥所以P(A∪B∪C)=P(A)+P(B)+P(C)=0.2+0.1+003=0.33,即至少遇到4个红灯的概率为0.33(3)设事件D为遇到6个及6个以上红灯,则至多遇到5个红灯为事件D.则P(D)=1-P(D)=1-0.03=0.97.即至多遇到5个红灯的概率为0.97

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