This is a function that will return with the confidence interval, using the average of a population, based on a normal distribution. The calculation requires having data that looks like this:

Click on an empty cell (1), and type in the confidence formula which is =CONFIDENCE(A2; A3 ;A4) (2).

Note: The 0,23 is the alpha, while the 3,7 is the standard deviation and the 80 would be the commuters, which is an example of the size.