I once tried a scam "investment" site for fun, knowing that they are not going to last long and operate like a Ponzi scheme. Daily interest was about 3.6%. I figured out, using the "rule of 72", that if the site survived for more than 20 days I will have my ROI.
I was luck to join early and the site did survived for more than 20 days, and I withdrew everything. So I doubled the little investment of 0.01BTC to about 0.02+BTC. About a month later, the site closed down and many investors lost their BTC.
In short, almost all BTC investment at the moment are scams- please correct me by letting me know if there is any valid investment site....
That's a really amazing outcome, 7788bitcoin, I'm most surprised that they let you withdraw. Actually, your method could be applied to any kind of trading (set % target limit, follow strict plan @ target %). Nice!