To add to the bag of marbles analogy in the second video, the likelihood of winning different prizes (so marbles of different, winning colours in the bag) coming out is what determines RTP, but RTP is not quite the same thing as your chance of winning. Sticking with just white marbles lose, red marbles win, if I put 1 red marble in the bag for every 4 white marbles, that means in 1 in 5 drawn will be a winner. But to win, you have to win higher than your stake (or else it’s the classic loss disguised as win, of course), so let’s say pulling a marble out the bag is £1 a go but if you draw out a red marble you win £2, double your stake. That means a 20% chance of winning is actually a long term 40% RTP, because for every £5 in, £2 is paid out. Add some more marbles with other prizes, in different colours and different quantities, and you tune the RTP to whatever precise number you want.