As per standard rules, the European roulette table has 37 numbers, starting from 0, then 1 to 36 on which bets are placed. The wheel is divided into two colors, red and black. Hence, the red and black numbers change. To the right of zero in the arc, there are nine small numbers in black (2, 4, 6, 8, 10, 11, 13, 15, 17), and then nine big numbers in red (19, 21, 23, 25, 27, 32, 34, 36) on the outside.
Similarly, to the left of zero, there are nine numbers in black, (20, 22, 26, 28, 29, 31, 33, 35) and then there are nine numbers in red, (1, 3, 5, 7, 9, 12, 16, 18). All the numbers face towards the inner side of the roulette wheels. These are the probable chances on which the ball will land. There are rules which state that three standard arcs in the wheel where players place bets.(資料來源 )