问题如下:
The stock of AAA company has a 30% probability to rise every year, assume that every annual trial is independent from each other. If the stock meets the goal of rising more than 1 time in the next 3 years, what is the probability that it fails to meet the goal?
选项:
A.0.343
B.0.216
C.0.784
解释:
C is correct. Based on the corresponding formula:
p(x)=P(X=x)=(nx)px(1−p)n−x, n = 3 and p = 0.30.
p(1)=(3−1)!1!3!×0.31(1−0.3)2=(3)(0.3)(0.49)=0.441
p(0)=(3−0)!0!3!×0.30(1−0.3)3=(1)(1)(0.343)=0.343⋅
The required probability is: p(1) + p(0) = 0.441 + 0.343 = 0.784
提问,这道题为什么不用二叉树的方法去解题?