What is the mean number of days per month in the first three months of a common year?

In a common year, the first three months are January, February, and March. January has 31 days, February has 28 days, and March has 31 days. To find the mean number of days per month, you add the total days (31 + 28 + 31 = 90) and divide by the number of months (3). Thus, the mean number of days per month in the first three months is 30.