People in the past used to exchange goods for goods, known as barter system. Later, coins were invented which made business simpler. Around a hundred years ago, there were heavy metal coins, which were the only things known as money. Gradually, paper money, also known as notes came into use, which represented large amount of coins and made business fairly simple. Nowadays, cards made of plastic, known as credit and debit cards are used to pay a large or small amount of money. This obviates the use of notes and coins. Moreover, the electronic money has gradually taken over the modern business and we don't have to deal with the physical money in most of the cases. The evolution of money is still going on steadily, which can pave the way to a different form of money in the future. Can you predict what kind of money will be in use in the future, say in about fifty or hundered years from now?