海同学2021-04-28 18:44:07

An analyst is studying a stock that is currently trading at $35. The analyst estimates that there is 33% probability that the stock will trade at $50 after one year, a 20% probability that the stock will trade at $42, and a 47% probability that the stock will trade at $20. What is the volatility of this stock return? 答案是方差=E(X^2)=15.46%，有点晕了，均值是E(X)，第二个不是E(X^2)=15.46%吗？为什么用方差=E(X^2)-E(X)^2=15.46%-2%^2 算出来的波动率会不一样？