The world's four major trading currencies, the Japanese yen, the U. S. dollar, the British pound, and the European Union's euro, are all free to float against each other. What is this an example of?

The correct answer is floating exchange rate system

Floating exchange is a currency worth how much buyers are willing to pay for it. This is determined by supply and demand, which in turn are determined by foreign investment, import / export rates, inflation, and a host of other economic factors.