|
发表于 2004-11-28 04:16:00
|
显示全部楼层
Re:我的面试一些经验(希望大家也来多交流)
从答案看, 这两道题的数学模型是这样的
1.已知P(A)=30% P(B|~A)=30% 求P(B)
解:
P(B) = P(B,~A) = P(B|~A)*P(~A) = 21%
2.
已知
P(A)=25%
P(B)=25%
P(C)=25%
P(D)=25%
求
P(B|~A),P(C|~A,~B),P(D|~A,~B,~C)
解:
P(B|~A) = P(B,~A)/P(~A) = P(B)/P(~A) = 0.25/0.75 = 1/3
P(C|~A,~B) = P(C,~A,~B)/P(~A,~B) = P(C)/P(~A,~B) = P(C)/P(~A)/P(~B|~A) = 0.25/0.75/(2/3) = 1/2
或者P(C|~A,~B) = P(C,~A,~B)/P(~A,~B) = P(C)/P(~A,~B) = P(C)/(1-P(A)-P(B)-P(A,B)) = P(C)/(1-P(A)-P(B))0.25/0.5 = 1/2
P(D|~A,~B,~C) = P(D,~A,~B,~C)/P(~A,~B,~C) = P(D)/P(~A,~B,~C) =
P(D)/(1-P(A)-P(B)-P(C)-P(AB)-P(BC)-P(AC)-P(ABC)) = P(D)/(1-P(A)-P(B)-P(C)) = 1 |
|