More seriously: on the one hand, I would expect your husband to have more books in his office than I do in mine; research in mathematics doesn't really involve a lot of reading of books. (Articles, yes, but that doesn't entail permanent additions to one's library.) As far as books at home go, well, you two have me outnumbered. Even assuming a certain amount of overlap in your interests, I'd expect your joint library to be larger than mine.

Not that we're competing or anything....