a只选一个的话,选择stock market,因为收益更高,而且标准差更小,也就是风险更**如果建立一个portfolio,一样一半的话mean为 8*0.5+20*0.5=14%variance为 25%*25%*0.5*0.5+22%*22%*0.5*0.5+2*0.4*22%*25%*0.5*0.5=0.038725 希望对你有所帮助 您这20分还真不好挣啊a reasonable investor shouid choose stock market,because it h**e higher return and lower r**k(standard deviaiton)the mean of the portfolio composed of equal proportions in gold and stocks 8%*0.5+20%*0.5=14%the variance of the portfolio composed of equal proportions in gold and stocks 25%*25%*0.5*0.5+22%*22%*0.5*0.5+2*0.4*22%*25%*0.5*0.5=0.038725 20210311