Who decides which currency each country in the world uses?

the United Nations

each individual country

the European Union

the United States

Each individual country

Currency is determined within the sovereign borders of a country. However, many countries choose to use another country's currency to ease trade or to have a more stable form of currency. In the case of the European Union, the countries share a common currency in addition to having their own currency. The international bank creates exchange rates allowing for all of the currencies to exist together.

The answer is each individual country. International money conversation rates show how much one part of a currency can be swapped for another money. Currency exchange amounts can be fluctuating, in which case they change frequently based on a mass of factors, or they can be fixed to one more currency, in which circumstance they still float, but they move in together with the currency to which they are fixed.