Sells don't affect your average price, only purchases.
You may want to give this a bit more thought
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How selling changes my prices (costs)? I don't get it.
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Most people are probably only interested in coins still in their inventory.
If you buy 1 BTC for $10, sell it for $100, then buy another at $1000, do you consider your average price $505 or $1000?
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My bad, it was supposed to be Weighted Average instead of average price.
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How it works?
What if I sell?
How much does my bitcoins are worth?