在线求助：各位大大看看这道题 increase, 在线求助, price, trade

studyn

Share of ABC trade at USD 100, The probability of the price increase by USD10 is 30%, the probability of the price deacrease by USD10 is 70%. What are the mean and Standard deviation of the price after 2 days if price changes consecutive days are independent?

A. mean=70 SD=11.32
B. mean=70 SD=12.96
C. mean=92 SD=11.32
D. mean=92 SD=12.96


我根据Binomial :
                       121
          110
100                100
           90
                        81

121*30%+100*70%=106.3
100*30%+81*70%=86.7

106.3*30%+86.7*70%= 92.58

所以mean应该是c 或 d, 不知到这样对不对。 另外怎么算SD?
在线求助，谢谢