An excellent source can be found on the website of the Mathematical Association of America. It discusses the U.S. Constitution and its apportionment paradoxes.

http://www.maa.org/publications/maa-reviews/mathematical-theory-of-democracy

This site reviews a book on Elections and Voting.

http://www.maa.org/publications/maa-reviews/the-mathematics-of-elections-and-voting

This site reviews apportionment paradoxes.

http://www.cut-the-knot.org/ctk/Democracy.shtml