To find the average value of a set of numbers.
Add up all the values in the set and then divide by the number of items in the set.
For example, the average value of 15 and 6 and 12 is 30 + 12 + 24 divided by 3 which equals 66/3 = 22.
To find the average number of days in a month.
Add up the total days for each month in the year and divide by the number of months in the year.
365 days divided by 12 months = 30.416 days in an average month.