To convert from a probability to odds, divide the probability by one minus that probability. So if the probability is 10% or 0.10 , then the odds are 0.1/0.9 or '1 to 9' or 0.111. To convert from odds to a probability, divide the odds by one plus the odds.
The odds are always stated as a simplified ratio a : b, where a and b are positive integers and a "e b. (The larger number comes first.) Think of the sum a+ b as the total number of possibilities. If a : b are the odds in favor, then a is the number of favorable outcomes and b is the number of non-favorable.