system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do they decide how many dollars are in one Euro or vice versa?
gpt
The more people want to have Euros, the more they will be worth. If no one wants them, then they don't have any value.

Some reasons for wanting more Euro in general:

* You live in a Euro country, and own lots of houses. You also think that the market for houses is going to become worse, so you prefer to sell them while you can get a good price, and when you sell them you want to get money (not seashells or beavers or wishes).

* If interest rates in a Euro country go up, meaning that you get more money by keeping money in the bank. Then if you own lots of houses, even if you don't think the house market is going to become worse, you may want to sell them to get money instead, because money in the bank will earn you more than holding on to the houses.

Some reasons for wanting Euros over dollars:

* You are/live in a country that use Euro.

* You belive that the value of the dollar is going to go down, or that the value of the Euro is going to go up. (As said, acting on these beliefs, not wanting dollars and wanting Euros, trying to sell dollars and trying to buy Euros - if enough people do it, it will make the dollar go down and the Euro go up.)

Since there is a lot of such guesswork, called speculation or gambling, the value of a currency can change a lot. This can be difficult for the people in the country, because if their currency suddenly becomes worth little, then they can't buy things from other countries, and if their currency becomes worth a lot, then no other countries can afford to buy things they want to sell, and no tourists want to come there.

The governments work a lot on trying to control these things, but if a large part of the country's money is being speculated in then it's very difficult for the government. One big problem is that many countries want the people in that country to decide what they should do in the country, but if a lot of their money is in the hands of speculators, and people in the country want to do something that they think is good for themselves, but could possibly be bad for the currency, then all the speculators will dump the country's currency, so the country can no longer import and so on. This means that a vote in what the country does, that goes above all the people and the president is in the hands of unaccountable investors.

In order to avoid that, there are some countries that say that speculation in their currency is not allowed, they don't allow it to be taken outside of the country. There are others who decide that their currency has a fixed value, like saying that it is always worth 3 for every dollar, no matter what the dollar is worth.