Probability is the branch of mathematics concerning numerical descriptions of how likely an event is to occur, or how likely it is that a proposition is true. The probability of an event is a number between 0 and 1, where, roughly speaking, 0 indicates impossibility of the event and 1 indicates certainty. The measure of uncertainty is called theory of probability. To understand and measure the chance, we perform the experiments like tossing a coin, rolling a die and spinning the spinner etc. The experimental approach relies on the idea of simulating the real event and observing how often the various possible outcomes occur in the trial(s) in order to assess how likely any given outcome might be. Sometimes it so happens that we would have to predict the outcome without actually performing the actual experiment. The probability or likeliness of an event occurring, without actually conducting the experiment is called theoretical probability.