At first glance, are you using a date object for the key in the Exchange method, and a string as the key in the json? Is it as simple as getting the date in to a string of the right format to use as your key? More on reddit.com

Honestly, I've found American Express' exchange rate is very close to the market's value of the foreign exchange. In Canada, some banks like to round in their favor to further hurt you when it comes to the exchange rate. The quick and dirty way to estimate is to convert the purchase. In your case, 1440 BRL to GBP. Then multiple that GBP value by the Foreign Transaction fee. Quick example: Google conversion of 1440 BRL as of this post is 203.63 GBP. If your Foreign Transaction fee is 2.5% (guessing since that's what mine is), then you go 203.63 * 1.025 = 208.72. Factor in a bit of error/market fluctuation and round up to 210. This does not factor in any import fees or VATs if you're buying something physical and importing it; those would be extra. More on reddit.com

Okay so x is the amount of gp and y is the tokkul equivalent. x=y More on reddit.com

Currency is bought and sold on a market, just like the stocks. But the reason it is bought and sold is a little different.

If you or I want to get some currency from another country we just go to the bank and make the change. This only works on a small scale. If a company wants to acquire $100,000,000 USD and all they have is Canadian dollars, then they are kind of stuck.

They need to find someone who has American money and needs Canadian money. A currency market helps bring these people together. The reason that a company might need foreign currency is the same as the reason you might need it, because they want to buy something in that country. Or they might have profits in a foreign country and want to change them into their home currency.

Buying something from France requires euros, but I only have American money. My friend Bob is also American but he has an part of his company in France. The profits for that company are in euros and he would like to pay off his house in Miami. So Bob and I do a trade, USD for Euros, and we are both happy.

Now this works because Bob and I are friends. But what if I don't have any friends. It would work better if there was a place I could go to do these kinds of trades. At that place they would keep detailed records of trades that take place. Every trade is recorded and, in real time, the information is used to calculate the exchange rate that the currency is currently trading at. understand that the exchange rate does not set the price of the trades, rather the prices of the trades set the exchange rates.

The “price” of currency changes as there are more people who have it and want to get rid of it, or don’t have it and want to get it. In theory this relates to the amount of stuff you can buy with the currency. But it all comes back to the supply and demand of the currency.

Lets look at an example. Wall-mart wants to buy some Stools from China. The factory worker in China is paid in Yuan, and so is the guy who chopped down the tree for the wood. The Stool is sold in US$. So somewhere a conversation needs to happen. The kind of money we are talking about here is far to large just to walk into your local bank and change the money. So Wall-mart needs to buy Yuan, but they only have US$.

Wall-mart goes to a currency market and starts offering US$ for Yuan. At first no one is selling, so they offer more US$ for the same Yuan. This happens over and over and over each time the price goes up, until Wall-mart has all the Yuan it needs.

So the price of currency relates to supply of it (how much of it exists out there in the world) along with the demand for it (the requirement to purchase local goods in local money). So the demand for currency relates to the demand for goods or services from that country. Hence the tie in with GDP. Inflation relates to how much of that currency is going to be required to purchase that thing. So as it raises so to does demand.

All exchange rates relate to one another. So assuming you could hold supply and demand constant, then the answer to your second question is yes. If 100 USD = 102 CAD and 102 CAD = 50 Euros, then you can assume that 100 USD = 50 Euros. If you actually tried to make this trade you would encounter a problem. Your own personal demand for the currency (added with everyone else's) would affect it's price. So the moment you purchased the $102 CAD, it would alter the relative price of USD and CAD for everyone. So by the time you made it around to the start again the exchange rate for Euro to USD would not be where it started.

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