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Based on the odds, I would expect one $200 winner for every 2 $20 winners.
I did a (manual) count on pages 5, 10, 15, 20, 25, 30, 35, 40, 45, and 50 on
Big wins at FreeBitco.in:
I just won $20 at FreeBitco.in! 116 times
I just won $200 at FreeBitco.in! 2 times
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You assume every top winner will inform the world of his winning roll in that thread, but that can't be given for granted.
Out of all my top winning rolls I never wrote in that thread myself for example for laziness and/or not being interested in doing so - I never rolled out the top-tier $200 tho lol.