The statement: There is 9-ways to 4 couple to dance with each other, when nobody can dance with his/her own partner.
Is true or not? And why? How can one calculate this?
This means 4 girl and 4 boy, every boy can dance with 3 girl, but repetition should be subtracted, isn't it?
Thanks for the help!
Edit: Is this question the same?
Edit2.: The accepted answer solves my question how I wanted to solve it, Ross Millikan provided the simplest and most convenient solution.