The first thing to do is to consider only the top-rated horse in the race. You multiply the odds of the horse by the number of the horses in the race, then divide the number into the total bank to arrive at the amount to be bet. If the amount to be bet is no more than 1/40th of the bank, you back the horse regardless of the odds; if the amount to be bet is more than 1/40th of the bank, the horse must be 4/1 ($5) or more to become a bet. In any case, you back the horse each way.

For example, if the bank was $500, there were eight runners in the race and the horse to be backed is at $5 (4/1), the total amount to be bet is $15 (rounded down); therefore you would bet $7.50 each way.