Calendars

Student #1:  "Mrs. A, why do you use the number 31 for everything?  Our letters have to be 31 lines, our plays have to be 3 minutes and 31 seconds, your excitement level for every assignment is a 31.  Why?"
Me:  "If you can guess why, and there is a reason, I will give you an automatic "A" for the semester."
Student #2:  "Is it because there are 31 months in a day?"
(silence)
Me:  "31 months in a day?"
Student #2:  "Yea, except February?"
(silence)
Me:  "Repeat what you said."
Student #2:  "31 months in a day."
(silence)
(Me looking at student)
Student #2:  "Ha! I messed that up!  I meant to say 31 MONTHS in 1 DAY."