The likelihood of an event happening. Probability is often expressed on a scale from 0 to 1. Where an event cannot happen, its probability is 0 and where it is certain its probability is 1. It can also be expressed as a fraction or a percentage. The probability of scoring 1 with a fair dice is 1/6. The chance of rolling an even number is 3/6, or 50%. The denominator of the fraction expresses the total number of equally likely outcomes. The numerator expresses the number of outcomes that represent a 'successful' occurrence. Where events are mutually exclusive and exhaustive the total of their probabilities is 1.