问题
填空题
For a group of n people, k of whom are of the same sex, the expression 
yields an index for a certain phenomenon in group dynamics for members of that sex. For a group that, consists of 20 people, 4 of whom are females, by how much does the index for the females exceed the index for the males in the group ？（）
答案
参考答案：0.6
解析：
这20个人中，女性有4人，则男性有16人，所以根据题意可得该群体的女性和男性指数分别为：[*]；
[*]
所以其差为0.8-0.2=0.6。