How Many Friday the 13ths
Date: 9/12/96 at 21:15:31 From: Jim Smith Subject: How Many Friday the 13ths Is there a way to figure how many Friday the 13ths can occur in a given year?
Date: 9/13/96 at 12:59:5 From: Doctor Tom Subject: Re: How Many Friday the 13ths There's no clean, simple way to do this, since there's very little mathematical structure to the calendar - it's mostly political. For example, did you ever wonder why February got short-changed on days when there were plenty of months to "steal" the 31st day from? Well, Augustus Caesar didn't like the fact that Julius' month (July) had 31 days and his (August) had only 30, so he "stole" a day from February to make August have 31. You can get an answer to your problem, however. There are exactly 14 different calendars possible. January 1 can be any one of 7 days, and if you know whether there's a February 29th, you can work out what days are Friday the 13th for each of them. I've even seen "universal calendars" that consist of 14 copies of a calendar for a year and then a list of years that tells you which calendar to use. -Doctor Tom, The Math Forum Check out our web site! http://mathforum.org/dr.math/
Search the Dr. Math Library:
Ask Dr. MathTM
© 1994-2013 The Math Forum