问题如下图：为啥碰到equal weighted的deviation，答案都不推荐用那个简便形式求啊，是有什么问题吗？
选项：
A. 
B. 
C. 
解释：
NO.PZ2015121801000062 问题如下 A portfolio manager creates the following portfolio:If the two securities are uncorrelate the expectestanrviation of equal-weighteportfolio is closest to: A.14.00%. B.14.14%. C.20.00%. is correct.lσport=w12σ12+w22σ22+2w1w2ρ1,2σ1σ2=(0.5)2(20%)2+(0.5)2(20%)2+2(0.5)(0.5)(0.00)(20%)(20%)=(1.0000%+1.0000%+0.0000%)0.5=(2.0000%)0.5=14.14%{l}{\sigma _{port}} = \sqrt {w_1^2\sigma _1^2 + w_2^2\sigma _2^2 + 2{w_1}{w_2}{\rho _{1,2}}{\sigma _1}{\sigma _2}} \\ = \sqrt {{{(0.5)}^2}{{(20\% )}^2} + {{(0.5)}^2}{{(20\% )}^2} + 2(0.5)(0.5)(0.00)(20\% )(20\% )} \\ = {(1.0000\% + 1.0000\% + 0.0000\% )^{0.5}} = {(2.0000\% )^{0.5}} = 14.14\% lσport=w12σ12+w22σ22+2w1w2ρ1,2σ1σ2=(0.5)2(20%)2+(0.5)2(20%)2+2(0.5)(0.5)(0.00)(20%)(20%)=(1.0000%+1.0000%+0.0000%)0.5=(2.0000%)0.5=14.14% 这道题可以用之前讲的多个资产，求方差的公式么？那个的假设也是没个资产的权重都是一样，刚好和这道题相同方差的平方=（资产1方差平方+资产2方差平方）/2
NO.PZ2015121801000062问题如下A portfolio manager creates the following portfolio:If the two securities are uncorrelate the expectestanrviation of equal-weighteportfolio is closest to:A.14.00%.B.14.14%.C.20.00%.is correct.lσport=w12σ12+w22σ22+2w1w2ρ1,2σ1σ2=(0.5)2(20%)2+(0.5)2(20%)2+2(0.5)(0.5)(0.00)(20%)(20%)=(1.0000%+1.0000%+0.0000%)0.5=(2.0000%)0.5=14.14%{l}{\sigma _{port}} = \sqrt {w_1^2\sigma _1^2 + w_2^2\sigma _2^2 + 2{w_1}{w_2}{\rho _{1,2}}{\sigma _1}{\sigma _2}} \\ = \sqrt {{{(0.5)}^2}{{(20\% )}^2} + {{(0.5)}^2}{{(20\% )}^2} + 2(0.5)(0.5)(0.00)(20\% )(20\% )} \\ = {(1.0000\% + 1.0000\% + 0.0000\% )^{0.5}} = {(2.0000\% )^{0.5}} = 14.14\% lσport=w12σ12+w22σ22+2w1w2ρ1,2σ1σ2=(0.5)2(20%)2+(0.5)2(20%)2+2(0.5)(0.5)(0.00)(20%)(20%)=(1.0000%+1.0000%+0.0000%)0.5=(2.0000%)0.5=14.14%想象成了完全相同的两个资产，他们也不相关，应该没有分散效应啊，为啥不能直接理解成组合标准差保持一样
NO.PZ2015121801000062问题如下 A portfolio manager creates the following portfolio:If the two securities are uncorrelate the expectestanrviation of equal-weighteportfolio is closest to:A.14.00%.B.14.14%.C.20.00%.is correct.lσport=w12σ12+w22σ22+2w1w2ρ1,2σ1σ2=(0.5)2(20%)2+(0.5)2(20%)2+2(0.5)(0.5)(0.00)(20%)(20%)=(1.0000%+1.0000%+0.0000%)0.5=(2.0000%)0.5=14.14%{l}{\sigma _{port}} = \sqrt {w_1^2\sigma _1^2 + w_2^2\sigma _2^2 + 2{w_1}{w_2}{\rho _{1,2}}{\sigma _1}{\sigma _2}} \\ = \sqrt {{{(0.5)}^2}{{(20\% )}^2} + {{(0.5)}^2}{{(20\% )}^2} + 2(0.5)(0.5)(0.00)(20\% )(20\% )} \\ = {(1.0000\% + 1.0000\% + 0.0000\% )^{0.5}} = {(2.0000\% )^{0.5}} = 14.14\% lσport=w12σ12+w22σ22+2w1w2ρ1,2σ1σ2=(0.5)2(20%)2+(0.5)2(20%)2+2(0.5)(0.5)(0.00)(20%)(20%)=(1.0000%+1.0000%+0.0000%)0.5=(2.0000%)0.5=14.14%为何不能用50%*16%+50%*12%算出A，错在哪里？uncorrelate定说明相关系数＝0嘛？
NO.PZ2015121801000062 A portfolio manager creates the following portfolio: If the two securities are uncorrelate the expectestanrviation of equal-weighteportfolio is closest to: A 14.00%. B 14.14%. C 20.00%.
NO.PZ2015121801000062 14.14%. 20.00%. B is correct. lσport=w12σ12+w22σ22+2w1w2ρ1,2σ1σ2=(0.5)2(20%)2+(0.5)2(20%)2+2(0.5)(0.5)(0.00)(20%)(20%)=(1.0000%+1.0000%+0.0000%)0.5=(2.0000%)0.5=14.14%{l}{\sigma _{port}} = \sqrt {w_1^2\sigma _1^2 + w_2^2\sigma _2^2 + 2{w_1}{w_2}{\rho _{1,2}}{\sigma _1}{\sigma _2}} \\ = \sqrt {{{(0.5)}^2}{{(20\% )}^2} + {{(0.5)}^2}{{(20\% )}^2} + 2(0.5)(0.5)(0.00)(20\% )(20\% )} \\ = {(1.0000\% + 1.0000\% + 0.0000\% )^{0.5}} = {(2.0000\% )^{0.5}} = 14.14\% lσport=w12σ12+w22σ22+2w1w2ρ1,2σ1σ2 =(0.5)2(20%)2+(0.5)2(20%)2+2(0.5)(0.5)(0.00)(20%)(20%) =(1.0000%+1.0000%+0.0000%)0.5=(2.0000%)0.5=14.14%是用不到的么 迷惑我们的么
