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Number Theory

Basic Applications of Modular Arithmetic

Friday the 13th


How many days after January 13th is February 13th?

Note: January has 31 days.

If January 13 is a Monday, what day of the week is February 13?

If May 13 is a Friday, what day of the week (during the same year) is April 13?

If a non-leap year begins on a Monday, will it have a Friday the 13th?

If July 13 is a Friday, is August 13 a Friday?


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