 In Europe , the subject of probability was first formally developed in the 16th century with the work of Gerolamo Cardano , whose interest in the branch of mathematics was largely due to his habit of gambling . He formalized what is now called the classical definition of probability : if an event has a possible outcomes and we select any b of those such that b ≤ a , the probability of any of the b occurring is <formula> . However , his actual influence on mathematical scene was not great ; he wrote only one light tome on the subject in 1525 titled Liber de ludo aleae ( Book on Games of Chance ) , which was published posthumously in 1663 . 
