On the standard roulette wheel the numbers are not arranged consecutively. By design, they alternate between red and black and exactly opposite each other number is the corresponding higher and lower number.
All red numbers are opposite the black numbers.
The roulette wheel is kept spinning all the time and sped up once a game is about to begin. The croupier rolls a little ivory ball along the inner edge of the wheel in the opposite direction of its spin. As the wheel turns, the ball loses momentum and it bounces among the slots and finally falls into one of the numbered slots. Bettors can place their bets right up until the time the wheel slows down and the ball drops into place. The number that the ball rests on is the declared as the winning number for that game.