以下是引用allen0018在2006-7-10 23:46:00的发言: Q9: A gardener is going to plant 2 red rosebushes and 2 white rosebushes. If the gardener is to select each of the bushes at random, one at a time, and plant them in a row, what is the probability that the 2 rosebushes in the middle of the row will be the red rosebushes?
A. 1/12 B. 1/6 C. 1/5 D. 1/3 E. 1/2 key:b
我选的是d 我怀疑这2个白花布一样? 我是c1-3; 答案 怎么来的?
是这样做的,不要用组合 a,b,b,a; a,b,a,b; a,a,b,b; b,a,a,b;b,a,b,a; b,b,a,a;所以是 b,understand? -- by 会员 顾风 (2006/7/11 9:36:00)
我是这样做的,不知道方法是否正确 按照白红红白的顺序走的话,被选概率依次为1/4,1/3,1/2,1. 所以中间两个的概率应该是1/3*1/2=1/6... |