188****7003 · 2021年02月21日
NO.PZ2018062016000073
问题如下：
Given the probability distribution above, what is the standard deviation of return of stock A?
选项：
A.16%
B.8%
C.2.56%
解释：
A is correct.
Expected return of stock A=0.2*30%+0.6*10%+0.2*(-20%)=8%
Variance(RA)=0.2(30%-8%)2+0.6*(10%-8%)2+0.2*(-20%-8%)2=0.0256
Standard deviation(RA)=0.02560.5=0.16
老师好，根据图表先计算出E（A）是8，计算A的方差。如果直接套用方差公式即（Xa-EA）平方求和/n 还是可以算出来是242.67的，然后开根号standard deviation A 就是15.57%,对比答案的话也最接近16%，如果这样算的话选A是不是碰巧算对？可不可以这样计算呢，还是在存在权重的情况下不能直接带入方差公式？
NO.PZ2018062016000073 问题如下 Given the probability stribution above, whis the stanrviation of return of sto A.16% B.8% C.2.56% A is correct. Expectereturn of stoA=0.2*30%+0.6*10%+0.2*(-20%)=8%Variance(RA)=0.2(30%-8%)2+0.6*(10%-8%)2+0.2*(-20%-8%)2=0.0256Stanrviation(RA)=0.02560.5=0.16 如题
NO.PZ2018062016000073 问题如下 Given the probability stribution above, whis the stanrviation of return of sto A.16% B.8% C.2.56% A is correct. Expectereturn of stoA=0.2*30%+0.6*10%+0.2*(-20%)=8%Variance(RA)=0.2(30%-8%)2+0.6*(10%-8%)2+0.2*(-20%-8%)2=0.0256Stanrviation(RA)=0.02560.5=0.16 最后一步0.0256^0.5 这个0.5是为什么呢
NO.PZ2018062016000073 8% 2.56% A is correct. Expectereturn of stoA=0.2*30%+0.6*10%+0.2*(-20%)=8% Variance(RA)=0.2(30%-8%)2+0.6*(10%-8%)2+0.2*(-20%-8%)2=0.0256 Stanrviation(RA)=0.02560.5=0.16老师，请问variance(Ra)用的公式是哪个？我想不起来了。
No.PZ2018062016000073 (选择题) Given the probability stribution above, whis the stanrviation of return of sto正确答案是: A A 16% B 8% A is correct. Expectereturn of stoA=0.2*30%+0.6*10%+0.2*(-20%)=8% Variance(RA)=0.2(30%-8%)2+0.6*(10%-8%)2+0.2*(-20%-8%)2=0.0256 Stanrviation(RA)=0.02560.5=0.16 想请问一下老师这题最后一部算stanrviation的时候为什么是0.5次方?不是0.2次方？谢谢~
