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On the frequency of Friday the thirteenth

Published online by Cambridge University Press:  21 June 2021

P. Stanley
P. Stanley*
Affiliation:
7 Croft Road, Wilmslow, CheshireSK9 6JJ
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Extract

This article begins with a new look at earlier work on this topic and continues with the presentation of a graphical technique for the determination of the months of a year for which the 13th is a Friday.

It might be thought that the likelihood of the 13 th day of a month being a Friday is the same as that of the 13th being any other day, but this is not so. The full day/date repeat cycle is 400 years, this being the interval between century years which are leap years. The outcome of an extraordinary counting exercise some 50 years ago by a 13-year-old Eton schoolboy, S. R. Baxter [1, 2], was to show that, over this period, the 13th of a month will be a Friday at least once more than any other day. Of necessity, Baxter’s calculation was intricate and an independent confirmation was undertaken as a matter of interest. The 400-year period beginning 1 March 2014 was considered. The work is described in four stages.

Type
Articles
Information
The Mathematical Gazette , Volume 105 , Issue 563 , July 2021 , pp. 222 - 225
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Copyright
© Mathematical Association 2021

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References

Baxter, S. R., Friday the 13th, Letters to the Editor, The Times (4 March, 1970.)Google Scholar
Baxter, S. R., To prove that the 13th day of the month is more likely to be a Friday than any other day of the week, Math. Gaz. 53 (May 1969) pp. 127–129.CrossRefGoogle Scholar
Stanley, P., A four-hundred year calendar, Math. Gaz. 103 (November 2019) pp. 556–558.CrossRefGoogle Scholar