Probability is used to predict the likelihood that a particular event will occur in the future.
In general, we can divide probability into two forms.
Statistical probability
Statistical probability is based on data that we obtain, either data that has already been collected or data we obtain through experiments.
Already collected data
Here, the probability of an event is found by looking at statistics.
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Example: Statistically, every fifth student has a smartphone with a cracked screen. Therefore, the probability of the event that a randomly chosen student has a broken screen is 20 % or 0.2. (One may choose how to express the probability).
Experimental probability
Another type of statistical probability is when the probability is determined through experiments.
Combinatorial probability
In combinatorial probability, the probability is calculated based on the possible outcomes.
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Example: With a standard die there are 6 possible outcomes {1,2,3,4,5,6}. The probability of the event of rolling an even number is therefore 3 {2,4,6} out of 6 possible outcomes. Hence, the probability of the event “an even number” is: 1/2, 50 % or 0.5.