Geometric distribution

In probability, the geometric distribution with probability of success formula_1, written formula_2, is a discrete probability distribution defined on non-negative integers. It is used to model the number of trials needed to obtain a first success, where the probability of success of each trial is formula_1.
An example involving geometric distribution is the number of times a die needs to be tossed in order to get a first heads.
The geometric distribution is the discrete analogue of the exponential distribution.