Often games contain random features. In poker and other card games, the first move is made not by the players but by the dealer who deals the cards randomly. Outcomes depend on the players' moves and on random elements. Even some completely deterministic games, like ROCK-SCISSORS-PAPER, are best played using some random device. Accordingly, we need to discuss the theory of probability.

Terminology

Much mathematical reasoning is concerned with trying to predict outcomes. If I create a sphere of radius 20cm, how large will its surface area be? If I combine 20ml of a 20% acid solution and 30ml of a 50% acid solution, what is the strength of the solution I get? What will be the speed of a falling apple 0.1 seconds after it is dropped? If a roulette ball has an initial speed of 3 meter per seconds, a given initial direction, and the roulette wheel is spinning at a certain speed, where will the ball end? If interest rate increases by 5% and productivity by 3%, how will the unemployment rate change? In many situations, models from the sciences, social sciences, or economics are not strong enough to predict these outcomes. Or, the models may be accurate, but the data available is not sufficient, which is the case in the roulette example. In those cases, outcomes seem random or unpredictable.