explained by the fact that after the valuation of currencies throughout the world moved away from 'gold standards', the prices of currencies started to be pegged against the US dollar, and other currencies fluctuated upwards or downwards as they related to this currency in a range of not more than a single percentage.
Hence, this was the start of foreign exchange rates and it was commonly referred to as fixed exchange rate. Since these changes in the method that the trade is carried out in recent times, both the fixed exchange rates and the gold standard have been abandoned so the exchange rates are now typically known as fluctuating exchange rates.
In reality it means that presently exchange rates are influenced by the forces of the market and when demand for a specific currency exceeds its supply then the exchange rates will end up going higher for the currency being demanded, and the opposite would occur should the demand decrease.
Now that the US dollar is the base currency in trading, the US government merely prints additional dollars and then sells these new dollars to various countries in the form of debts, though due to rising oil prices as well as stronger world economies, currently the US dollar is losing its vice like grip as the predominant currency of the world which is eroding the exchange rates of the dollar and the United States closest trading allies are affected as well.
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