What year was probability discovered?

Answer 1

Probability is a concept that cannot be "discovered." The concept of probability is ingrained in any complex organism's thought process through evolution and has been ever since complex thought evolved. To survive, animals are constantly taking statistics, weighing odds, figuring out what course of action will lead to survival. For example, an owl might hunt at night and decide to target a certain area of hunting ground, deciding that it is more probable that prey might be found in that area.

However, as a formal category of mathematics, theories regarding probabilities can be developed or "discovered." See the related question below.