The language of odds such as "ten to one" for intuitively estimated risks is found in the sixteenth century, well before the development of mathematical probability.[4] Shakespeare wrote:
Knew that we ventured on such dangerous seas
That if we wrought out life 'twas ten to one
— William Shakespeare, Henry IV, Part II, Act I, Scene 1 lines 181–2.
The sixteenth century polymath Cardano demonstrated the efficacy of defining odds as the ratio of favourable to unfavourable outcomes (which implies that the probability of an event is given by the ratio of favourable outcomes to the total number of possible outcomes
https://en.wikipedia.org/wiki/Odds
probability for something =odds for something /( odds for something +1)
So 3 to 1 is 75% for vs 25% against or 3/(3+1)=75% for.