Choose the number of horses in a given race that you want to bet on.
Calculate each horse's odds of winning by dividing the number 100 by the given odds. For instance, a horse with odds of 4.5 to 1 would have a 22.22% chance of winning: 100 / 4.5 = .2222.
Add the percentages together of all the horses you plan on betting on. This amount is the overall chance that one of the horses you have chosen will win the race. Using the example cited in the Horse Racing Systems website, in a situation where you've chosen three horses, you would show calculations as follows:
Horse A = 28.57% (100 divided by 3.5 equals 28.57)
Horse B = 25% (100 divided by 4 equals 25)
Horse C = 20% (100 divided by 5 equals 20)
28.57 + 25 + 20 = 73.57%
Divide the horses' individual percentage by the overall percentage and then multiply this amount by the total amount of money you want to bet on the race.
Again, using the Horse Racing Systems' example, with modifications of dollars for British pounds:
Horse A = 28.57 / 73.57 x $20 = $7.76
Horse B = 25 / 73.57 x $20 = $6.80
Horse C = 20 / 73.57 x $20 = $5.44
Total stake = 7.76 + 6.80 + 5.44 = $20