最爱银杏飘
I think something is wrong with the problem. no key to the problem therefor choose A at most 47 had breakfast. 12 had eggs bacon and toast4 eggs and toast 3 had bacon and toast 7 had eggs and bacontotal 23 eggs 22 bacon 19 toast 4eggs ang 17toast were rest A guest is selected at random only eggs and toast no bacon eliminate C,D and B therefor choose A
饭兜兜兜得牢
7) A box contains 3 red, 4 white and 5 blue discs. 7 ）中包含3红， 4白色和蓝色光盘5 。 Three discs are selected at random三盘随意挑选的 from the box.从盒子。 Find the probability that:找到的概率： a) all three discs are the same colour, if the selection is with replacement a ）所有三个光盘是相同的肤色，如果选择与更换 b) all three discs are of different colours, if the selection is without replacement b ）所有三个光盘不同的颜色，如果选择不更换
天可莲见
额````翻译楼上的已经做了，我就直接解答了。a、颜色相同有3种情况，我们要分别计算就是1/4*2/11*1/10+1/3*3/11*1/5+5/12*4/11*3/10=3/44就是这个概率啦~b、这个跟上面挺像的，就是有点麻烦1/4*4/11*1/2+1/4*5/11*2/5+1/3*3/11*1/2+1/3*5/11*3/10+5/12*3/11*2/5+5/12*4/11*3/10=3/11真是累人，就是要分情况讨论，倒不是很难，就是不同顺序的搭配
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