Probability is the measure of the likelihood that an event will occur. Basically it is quantified as a number between 0 and 1, where 0 indicates impossibility and 1 indicates certainty. A very simple example is the tossing of a coin that has two sides: head and tail. We can describe the probability of this event in terms of the observed outcomes or the expected results.
For a "fair" coin, the probability of head equals the probability of tail. However, for an "unfair" or "weighted" coin the two outcomes are not equally likely.
Use the following simulation to observe the outcomes of tossing a coin.