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Comment by thaumasiotes | Hacker News Reader

> "With cockroaches, you can invest 20 yuan and get back 150 yuan," or $3.25 for a return of $11.

?????????

As I see it, 150元 is seven and a half times as much as 20元. I didn't use any exchange rate of any sort to compute that.

Seven and a half times $3.25 is $24.375 . Using the most charitable interpretation I can think of, that's a return of $21.12 on an investment of $3.25, but put in the same terms as the original quote, I'd call it investing $3.25 and getting back $24.38. What happened there?

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Maybe the bid-ask spread in that area for USD is that wide :D You might see something like this

        BUY       SELL
  USD   6.1538    13.3636

And it makes sense immediately. You have USD3.25, you buy 20元 for that. Pay for various resources, get back 150元. Well, you can get only USD11 for that.

Yes, you seem to be correct. Good catch. According to a google for "150 CNY in USD", "150 Chinese Yuan equals 24.59 US Dollar"

Well sure, but even if 150 chinese yuan were equal to 11 USD, turning 20 yuan into 150 yuan wouldn't be like turning $3.25 into $11, it would be like turning $3.25 into $24.375. It might be metaphysically more like turning $1.47 into $11, but absolute quantities aren't really at issue when you're talking about return rates (I'm assuming the cockroach farm, which by implication earns in the tens of thousands of USD per year, can scale up beyond a return of 150 yuan). It would have been easier and less of a gaffe for the reporter to say "you can invest 20 yuan and get back 150 yuan, or $20 for a return of $150". Why did they bother to print a conversion at all?

There is some logic in the conversion as it helps show scale - if you run a lemonade stand it may be true to say you can invest $10 and profit $20, but not true that you could invest $1m and profit $2m, whereas in a car manufacturing business you might be able to invest $Xm and profit $2Xm, but investing $10 is unlikely to give you any return. These two scenarios can't both be explained as "you can invest 1 and get 2 back".

That said, a single quote, even with conversion, doesn't help much here - if a reader wanted to start a farm now it doesn't give them any idea of whether 20 yuan is the minimum or the maximum investment (I presume it's below the minimum anyway).

The article already indicates (in USD figures) that a cockroach farm generates in the low tens of thousands of USD per year.

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