NO.PZ2018062016000082
问题如下:
The stock of AAA company has a 30% probability to rise every year, if every annual trial is independent from each other, the probability that the stock will rise more than 1 time in the next 3 years is:
选项:
A.0.145
B.0.216
C.0.377
解释:
B 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(2)=(3−2)!2!3!×0.32(1−0.3)1=(3)(0.09)(0.7)=0.189.
p(3)=(3−3)!3!3!×0.33(1−0.3)0=(1)(0.027)(1)=0.027⋅
The required probability is: p(2) + p(3) = 0.189 + 0.027 = 0.216
我算的是接下来3年均大于, 也就是p1+p2+p3均大于的情况, 请问这样理解为什么不对