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　　）theNationalFootballLeagueplayoffsarejustabouttobegin.Becauseoftheirgreatrecordintheregularseason,theSteelersgetabyeintheregularseason,theSteelersgetabyeinthefirstweekoftheplayoffs.Inthesecondweek,theywillpl

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　　theNationalFootballLeagueplayoffsarejustabouttobegin.Becauseoftheirgreatrecordintheregularseason,theSteelersgetabyeintheregularseason,theSteelersgetabyeinthefirstweekoftheplayoffs.Inthesecondweek,theywillplaythewinnerofthegamebetweentheRavensandthePatriots.AfootballexpertestimatesthattheRavenswillbeatthePatriotswithprobability0.45.ThissameexpertestimatesthatthatiftheSteelersplaytheRavens,themeanandstandarddeviationofthepointspread(SteelerspointsminusRavenspoints)willbe6.5and10.5,whereasifthesteelersplaythePatriots,themeanandstandarddeviationofthepointspread(SteelerspointsminusPatriotspoints)willbe3.5and12.5.Findthemeanandstandarddeviationofthepointspread(Steelerspointsminustheiropponent'spoints)intheSteelersgame.

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2020-11-30 11:29

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沙朝锋

　　期望值是6.5*0.45+3.5*0.55=4.85.方差是：根据条件方差的计算公式D(X|A)=E(X^2|A)-E(X|A)^2,得E(X^2|A)=D(X|A)+E(X|A)^2=10.5^2+6.5^2同理E(X^2|B)=D(X|B)+E(X|B)^2=3.5^2+12.5^2所以,D(X)=0.45*(6.5^2+10.5^2)+0.55...

2020-11-30 11:31:55

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