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標題:
probability
發問:
Mr and Mrs Lee want to have at least a son and a daughter. how many children should Mrs Lee give birth to so that the probability of having a son and a daughter is more that 0.9? 更新: 為什麼要1- 解釋一下條式?
最佳解答:
Let x be the required number of children :P(at least a son and a daughter among x children) > 0.91 - P(x boys) - P(x girls) > 0.91 - (1/2)^x - (1/2)^x > 0.90.1 > (1/2)^(x - 1)log 0.1 > (x - 1) log (1/2)- 1 > (x - 1) (- 0.30103) 3.322 4.322Mrs Lee should give birth to 5 children. 2011-06-06 18:02:12 補充： 一仔一女的反面是全仔或全女, 所以 一仔一女機會 + 全仔或全女機會 = 1 1 - 全仔或全女機會 = 一仔一女機會
其他解答:
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