Tedious experimentation! How else do we figure out stuff about this game?
For a standard, standard game at most difficulty levels, Representation is an effective 40% discount on the 10% per-city penalty, but that was not the case in vanilla (originally 30%) or pre-BNW-patch (15%), where Representation's -33 integer discount would, if left unrounded, result in a per-city social policy cost of 20.1% and 10.05%, respectively. I suspect Firaxis didn't want those minor decimal amounts cluttering up the computation -- hence, the Representation rounddown -- but they didn't revise that approach when they changed standard to a 10% per city penalty.