Tree diagram

2013-02-28 5:04 pm

Assume identical twins are always of the same sex, equally likely boys or girls.
Assume that for fraternal twins the firstborn is equally likely to be a boy or a girl, and so is the secondborn, independently of the first. Assume that proportion p of twins
are identical, proportion q=1-p fraternal. Draw a tree diagram to illustrate this.

更新1:

Find 1. P(firstborn boy and secondborn girl) 2. P (secondborn girl I firstborn boy) 我試用過tree diagram 但計吾岩吾該解釋ー下點計

回答 (1)

50418129

2013-02-28 6:18 pm

✔ 最佳答案

the diagram are as follows:

圖片參考：http://imgcld.yimg.com/8/n/HA00108663/o/20130228101755.jpg

2013-02-28 14:08:07 補充：
(1)

P(firstborn boy and secondborn girl)
= 1/2 x (1 - p) x 1/2
= (1 - p)/4

(2)

P(secondborn girl I firstborn boy)
= P(secondborn girl and firstborn boy) / P(firstborn boy)
= [1/2 x (1 - p) x 1/2] / (1/2)
= (1 - p)/2

參考: knowledge

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