How do you express probabilities?

Answer 1

Probabilities are expressed a few different ways, often depending on the means of calculating the probability.

Theoretical probabilities are generally calculated as the number of successes divided by the total number of possibilities. For example, rolling a number greater than 4 on a die has two successes (5 or 6) and six possibilities (1, 2, 3, 4, 5, or 6). Because each of these outcomes is equally likely to occur, the probability is 2/6 = 1/3. Probabilities calculated in this way are typically expressed as fractions, although they can also be expressed as decimals or percents (more commonly referred to as the chance of an event occurring).

Probabilities based on the normal curve, models, random variables and the like are generally expressed as decimals, although percentages are also acceptable.

Note that for all of these forms, probabilities are always between 0 and 1 inclusive (0% and 100%). A probability of 0 (0%) has absolutely no chance of occurring while a probability of 1 (100%) means an event is certain to occur. Probabilities in between represent a certain degree of likelihood of the event occurring.