[理工] [機率] 一題條件機率

[aj0938 (Daniel)]

From families with three children,a family is selected at random

and found to have a boy. What is the probability that the boy has

(a)an older brother and a younger sister (b)an older brother

(c)a brother and a sister? Assume that in a three-child family

all gender distributions have equal probabilities.

a小題答案是1/14 b小題是13/42 c小題是3/7

感謝幫忙回答的人

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◆ From: 114.39.24.233
※ 編輯: aj0938          來自: 114.39.24.233        (08/02 15:34)
→ mcu68104:我算成一開始有8種可能，知道一個男生所以7/8，然後a有
→ mcu68104:1種，bc各3種情形，結果是1/7 3/7 3/7 = =錯很大的樣子..
→ cha122977:我算的答案跟樓上一樣...
→ cha122977:第一題的我覺的很怪 因為樣本空間只有八種
→ cha122977:為什麼分母會出現14...="=(還是我誤解題意?)
→ cha122977:另外一種想法是1/12 5/12 6/12...也不同= 3=