r****t
发帖数: 10904 | 1 There are two boys and three girls in a room. Now put one more baby. A
nurse randomly picked a baby and it is a boy. So what is the chance, the
new baby who are added are boy?
http://www.mitbbs.com/article/Quant/31266011_0.html
那里给的解答：
A: added one is boy
B: picked one is boy
P(A|B)== P(B|A) P(A) / P(B)=(1/2*1/2)/(1/3+1/2)=3/10
sunmountain 说 (1/2)/(1/2+1/3)=3/5
疑问：这里是不是假设了 P(A)=1/2 or P(A) = 1？
觉得做这种假设都不合理，P(A)/P(B) 应该是多少？ |
d**0
发帖数: 124 | 2 没看到解答 这个题你就分两个情况
A:加的是boy
B：加的是girl
然后根据条件概率公式列一下就可以算出来 结果是3/5。 应该隐含的假设就是A，B发
生的概率相同。
楼主是要面ms吧 这题是前两年hr电话第一轮经典题啊 很多人都被问到了
【在 r****t 的大作中提到】
: There are two boys and three girls in a room. Now put one more baby. A
: nurse randomly picked a baby and it is a boy. So what is the chance, the
: new baby who are added are boy?
: http://www.mitbbs.com/article/Quant/31266011_0.html
: 那里给的解答：
: A: added one is boy
: B: picked one is boy
: P(A|B)== P(B|A) P(A) / P(B)=(1/2*1/2)/(1/3+1/2)=3/10
: sunmountain 说 (1/2)/(1/2+1/3)=3/5
: 疑问：这里是不是假设了 P(A)=1/2 or P(A) = 1？
|
s*******0
发帖数: 3461 | 3 你的p(B) 算错了
需要用全概率公式 p(B)=P(B|A1)*P(A1)+P(B|A2)*P(A2) |
r******g
发帖数: 13 | 4 conditional probability should be no less than the joint probability (P(A|B
)>= 1/2)
P(A,B) = 1/2, P(~A,B) = 1/3, P(B) = 5/6, P(A|B) = P(A, B)/(P(B) = 3/5,
【在 r****t 的大作中提到】
: There are two boys and three girls in a room. Now put one more baby. A
: nurse randomly picked a baby and it is a boy. So what is the chance, the
: new baby who are added are boy?
: http://www.mitbbs.com/article/Quant/31266011_0.html
: 那里给的解答：
: A: added one is boy
: B: picked one is boy
: P(A|B)== P(B|A) P(A) / P(B)=(1/2*1/2)/(1/3+1/2)=3/10
: sunmountain 说 (1/2)/(1/2+1/3)=3/5
: 疑问：这里是不是假设了 P(A)=1/2 or P(A) = 1？
|
g*********r
发帖数: 2847 | 5 you cannot solve the problem unless assumptions are made, such as mentioned
by dp70 on the 2nd floor. |
M*******r
发帖数: 165 | 6 It should be:
P(B)=1/2*P(A)+1/3*(1-P(A))=(1/2*1/2)+(1/3*1/2)=5/12 |
