Probability is a statistical measure of the chance that an event will occur. An event, in probability, describes a set of outcomes. So for example, when two die are rolled, the events (the sums of the numbers) that may happen are: 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12. It can be seen that 1 is not an event as a minimum of 1 must be rolled on each die. However, each event is not associated with the same probability as some of the numbers are more likely to be rolled.
For example, the sum of the numbers equaling 2 has the probability of 1/36 to be rolled – this is because there is only one combination of die rolls out of 36 which can add up to 2. On the other hand, the sum of the numbers equaling 7 has the probability of 6/36 to be rolled – this is because there are 6 combinations of die rolls out of 36 which can add up to 7. These are (1+6), (6+1), (2+5), (5+2), (3+4), (4+3).
The probability of an event is commonly written as the number of outcomes that constitute the event divided by the total number of possible outcomes, which for the number 7 is 6/36 = 1/6. Thus, it can be seen that understanding probability is a practical skill for everyday life.