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Friday the 13th

Posted By: Nack Ballard
Date: Saturday, 14 May 2011, at 1:57 p.m.

In Response To: Friday the 13th (Bob Koca)

Under the current calendar system the long run proportion of 13ths that are Friday is

a) 1/7 b) greater than 1/7 c) less than 1/7

Interesting problem!

I believe the answer is (b); in other words, that in each and every 400-year cycle Friday is the most likely day of the week to coincide with the 13th. Sunday and Wednesday are –1 (i.e., one fewer), Monday and Tuesday are –3, and lucky Thursday and Sunday are –4.

Nack

Messages In This Thread

• Friday the 13th
  Bob Koca -- Friday, 13 May 2011, at 7:22 p.m.
  • Friday the 13th
    Stein Kulseth -- Friday, 13 May 2011, at 9:39 p.m.
  • Friday the 13th
    Rich Munitz -- Friday, 13 May 2011, at 10:35 p.m.
    • Friday the 13th
      Casper van der Tak -- Friday, 13 May 2011, at 10:49 p.m.
      • Friday the 13th
        Bob Koca -- Friday, 13 May 2011, at 10:50 p.m.
        • Friday the 13th
          Casper van der Tak -- Friday, 13 May 2011, at 10:55 p.m.
          • Friday the 13th
            Stein Kulseth -- Friday, 13 May 2011, at 10:59 p.m.
            • Friday the 13th
              Casper van der Tak -- Friday, 13 May 2011, at 11:04 p.m.
            • The Gregorian Calendar
              David Rockwell -- Saturday, 14 May 2011, at 1:12 a.m.
              • The Gregorian Calendar
                ah_clem -- Saturday, 14 May 2011, at 1:52 a.m.
                • The Gregorian Calendar
                  David Rockwell -- Saturday, 14 May 2011, at 2:26 a.m.
                  • The Gregorian Calendar
                    Timothy Chow -- Saturday, 14 May 2011, at 2:47 a.m.
                    • The Gregorian Calendar
                      David Rockwell -- Saturday, 14 May 2011, at 11:11 p.m.
                      • The Gregorian Calendar
                        Sam Pottle -- Sunday, 15 May 2011, at 1:10 p.m.
                      • The Gregorian Calendar
                        Elliott Winslow -- Wednesday, 18 May 2011, at 4:02 a.m.
                • The Gregorian Calendar
                  Casper van der Tak -- Saturday, 14 May 2011, at 4:53 a.m.
                • The Gregorian Calendar
                  Rich Munitz -- Saturday, 14 May 2011, at 3:00 p.m.
    • Friday the 13th
      Stein Kulseth -- Friday, 13 May 2011, at 10:58 p.m.
  • Friday the 13th
    Nack Ballard -- Saturday, 14 May 2011, at 1:57 p.m.
    • Friday the 13th
      Casper van der Tak -- Saturday, 14 May 2011, at 2:23 p.m.
      • Friday the 13th
        Nack Ballard -- Tuesday, 17 May 2011, at 4:19 p.m.
        • Friday the 13th
          Casper van der Tak -- Tuesday, 17 May 2011, at 5:13 p.m.
      • Friday the 13th
        ah_clem -- Monday, 23 May 2011, at 4:04 p.m.
        • Friday the 13th
          Casper van der Tak -- Monday, 23 May 2011, at 4:32 p.m.
          • Friday the 13th
            ah_clem -- Tuesday, 24 May 2011, at 1:47 a.m.
            • Friday the 13th
              Casper van der Tak -- Tuesday, 24 May 2011, at 7:30 a.m.
  • Friday the 13th
    garyo -- Saturday, 14 May 2011, at 4:58 p.m.