What is the mean of 1 2 3 4?

The mean, or average, of a set of numbers is calculated by adding all the numbers together and then dividing by the total number of values. In this case, the sum of 1 + 2 + 3 + 4 is 10. Since there are 4 numbers in the set, the mean is 10 divided by 4, which equals 2.5. Therefore, the mean of 1, 2, 3, and 4 is 2.5.