If you had $100 to invest online, where would you put it for best return?

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So, let's say you have $100. What would you put the money in, so that you'll get more than $100 in some time? If $100 is too small of an investment, what about $100 every month, what would you do with such money online so you would earn even more per month? Would you buy referrals for a program? Would you advertise a program? Would you buy advertising for your blog? Invest in Forex? What's the most profitable return of investment? Share your good ideas please :)