Numbers of days in each month?

Answer 1

There are 7 months with 31 days, 4 months with 30, and 1 with 28 (most years) - therefore the mode is the number which appears the most: 31.

Answer 2

30 days in September, April June and November, all the rest have 31 days except February which has 28 days and 29 days in a leap year.