主题：有人会做这道题吗

identical twins come from the same egg and hece are of the same sex.fraternal twins have a 50-50 chace of being of the same sex.among twins,the probobility of a fraternal set is p and an indentical set is q=1-p.if the next set of twins are of the same sex,what is the probobility that they are identical 答案是2q/(1+q)

有没有人可以先帮我翻译一下,再大概告诉我大致思路

实际上就是Bayes公式的应用,同卵双胞胎同性概率为1，异卵同性概率为1/2，而异卵双胞胎的概率是p，同卵概率是q＝1－q。求在同性的情况下，同卵的概率是？

记A为同性事件，B为同卵事件，所求P（B|A）＝P(A|B)*P(B)/[P(A|B)*P(B)+P(A|B' )*P(B' )]