There are some casino games where there's nothing you can do to change the outcome. They include: Slots Bingo Scratch cards Roulette These online games use Random Number Generators. Therefore, nothing you do can sway the outcome. For slots, the return to player percentage is the figure that is paid out to players over time. This is based on thousands of spins. All RTPs are less than 100%. The remaining percentages are what the online casino expects to make off wagers on that particular game.