Which day of the week (Sunday, Monday, etc.) is the probability largest to fall on the 13th of a random month, in a random year?

Or is this probability the same for each day of the week?

There are 7 non-leap year calendars and 7 leap year calendars. I figured that I could just tally the 13ths in the 7 non-leap years, multiply by 3 and add the leap year 13ths. Trouble is, or maybe not, I get 12 13ths for each day of the week in non-leap years, AND 12 in the leap years. Unless my brute force counts are wrong, I get 24 13ths for each and every day. I have to say that the propability is the same for each day of the week.<br><br>
If you write a program to scan a period of years, you will get  different totals depending on where you start and stop.

Posted by bob909 on 2004-09-07 05:02:50