Originally Posted by TheAgent

if you have large amount of money you can do currency arbitrage

For example:
if $1.00 in U.S. currency buys 0.7 British pounds currency
£1 in British currency buys 9.5 French francs
1 French franc buys 0.16 in U.S. dollars, then an arbitrage trader can start with $1.00 and earn

1 x 0.7 x 9.5 x 0.16 = 1.064 dollars which means profit of 6.4 percent.