Floated currencies are NOT based on national GDP and that sort of thing. They are based on the price that someone is willing to pay and someone is willing to sell. I.e. if someone will spend 1 AUD to buy 1 USD, and someone is willing to sell 1 USD for 1 AUD then the price of 1 USD is 1 AUD. This is completely unrelated to GDP (although GDP might be used as a marker of confidence that indicates security of currency investment).
