2. Bet $20000 on black at the casino, if you win, well done. If you lose, you lost $30000.
There is 75% chance to make $10000 - casino edge using this strategy. You can do this on any day of the week the casino is open.
Trouble is, even when the chance of losing is 0.25%, you'll lost once every 400 games.
And at one point, the loss will be greater than all the money you had.. and there's no coming back from that.
Given the chance of winning a round is p=0.5, the chance of losing is q = 1 - p = 0.5
If you've lost the first round, the odds of you twice in a row are q = 0.5^(2 rounds) = 0.25
Which means the odds of you winning are p = 1 - q = 1 - 0.25 = 0.75.