To compute your $2 win price, take the odds of your horse and multiply the first number by 2, divide that by the second 2/5, 2/1, 9/1.
Whenever you see two numbers separated by a slash, i.e. this is a fractional betting odd. Betting odds allow you to calculate how much.
European odds multiplied by your stake equals the payout. The odds show how You may hear the expression 2/1 on referring to a selection with odds of 1-2. The Witcher in 5 Minutes