Permutation or combination
Three pairs of twin women are each married to twin men in such a way that each woman's twin sister is married to her husband's twin brother. if all twelve of them enter a mixed doubles tennis tournament, in how many ways can they be arranged as six matched pairs. (i.e. in each pair there is one woman and one man.) so that no one is pair with their spouse or their twin's spouse?
I wouldn't even know where to start..this problem is giving me a headace. Can someone please help and explain it to me. Thank you