数学狗狗第2题求助

yhj_8888

1.   男生4人, 女生4人, 被分为两组, 一组全是男生的概率是多少.  


1/ [C(8,4)] = 1/70;  1/ [C(8,4)/A(2,2)] = 1/35


请问这个题的答案到底是 1/70还是1/35啊？
我倾向于1/70，因为两组没有区别呀，4男4女分为两种只有一种情况，没有4男为第一组或第二组

求NN 解释

sdcar2010

1/35 is the answer.

Total possibilities = 70 for choosing 4 members out of 8. Two of them: either all male or all female in the chosen 4 will fulfil the requirement of one group is all male.