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I need a math refresher. Say I purchase a stock for $100 and sell it for $150. That's a 50% profit, right? But if I divide 150 by 100, I end up with 150% profit. What am I doing wrong?

Also how do I figure time into the equation (i.e. opportunity costs). Say I purchase stock A at $100, hold it for 10 days and sell it for $150. And I purchase stock B for $100, hold it 100 days and sell it for $150. Common sense tells me that they are not equally profitable, but I can't figure out how to prove this mathmatically.

These are simple questions that could be answered by anyone. But by asking them this way, I'm able to hide behind my user name and not own up to my inherent ignorance.

Thanks for your help.
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