[理工] 機率
1.
A ordinary deck of 52 cards is dealt,13 each,at random
among A,B,C,and D.Waht is the probability that A and
B together get two aces?
我一開始是算4C1*48C12*3C1*36C12/52C13*39C13
但解答給的是4C2*48C24/52C26
為什麼他是一起考慮???是因為"together"這單子嗎??
A and B一起取這樣??
2.
From the set of all families with two children,(a)a family is selected
at ranndom and is found to have a girl,what is the prob. that the
other child of the family is a girl?,(b) a child is selected at random
and is found to be a girl,what is the prob. that the second child of
this girl's family is also a girl? Assume that in a two-child family
all sex distributions are equally probale.
答案分別是(a) 1/3,(b) 1/2
想請問一下這兩題問的差異在哪裡?
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