The greatest probability—the certainty that an event will occur—is 1. Thus, a probability of 1 means that the event must occur. For example:
The probability that you roll a fair die once, and it lands on a number less than seven, is certain, or 1:
As a percent, this certainty is expressed as 100%.
The lowest probability—the impossibility that an event will occur—is 0. Thus, a probability of 0 means that an event will NOT occur. For example, the probability that you roll a fair die once and it lands on the number 9 is impossible—a probability of 0:
As a percent, this impossibility is expressed as 0%.
Thus, probabilities can also be expressed as percents between 0 percent and 100 percent, inclusive, or fractions between 0 and 1, inclusive.