Another task that Cortana can accomplish, is the conversion of currency. Let's say you were offered a job that pays 1 million Japanese Yen. You might think that you've become a millionaire. But before you start bragging to friends and family, you should ask Cortana to convert Yen into Dollars. Perhaps you didn't know that currency fluctuates. Ask Cortana to convert 1 million Yen into U.S. Dollars and you will find out that your job is actually paying you under $9600.
Siri and Google Now have both been able to handle world time and currency conversions. But Windows Phone users have no reason to be jealous. After all, Cortana can handle the exact same tasks.