find the number of ways in which a mixed double game can be organized amongst 9 married couples if no husband or wife play in the same game ?

its simple 9*8=72

hi zaid ignore the previous post 

you can take the analogy of function mapping 

take 9 husbands as X and 9 wives as Y   X TO Y

now total number of ways in which the game can be organised is  total number of injections (P(9,9))

and there is only one way in which the husband and wives are pair together

so