There are 10 couples at party .In this question I have only doubt that if I chose 2 husbands first ,now for wives remaining choice will be 8 so it will be 10C2 *8C2 ,Now I could have done it other way around like first chosing 2 wives and then removing their corresponding husbands so again no of ways in which team can be formed is 10C2*8C2 ,now why can't we add these two cases ?