







Calendar arithmetic 
20160214 

From Jenalee: January 1, 2001 is Julian Day 2 451 911 (the number of days that have passed since Day 0, January 1, 4713 BC).
If Julian Day 0 was a Monday, what day of the week was January 1, 2001? Answered by Victoria West. 





On what day of the week did 1994 begin? 
20150405 

From tayyaba: there were 365 days in the year 1993
the first day of the year was friday.
on what day of the week did 1994 begin? Answered by Penny Nom. 





Your birthdays until your one hundredth 
20060909 

From Alan: which of your birthdays until your one hundredth, fall on the same day of the week as the day you were born? Answered by Chris Fisher. 





The day of the week 
20060319 

From Neil:
A friend of mine has an excellent memory for dates and events that occurred on that date, but his party piece is the ability to tell you the day of the week that fell of any given date. This talent is all the more extraordinary because the answer comes back in less than 2 seconds (often under 1 second). By his own admission he is no mathematician.
Now his memory and knowledge are without question, but I challenged him that because of its diversity this party piece could not be based upon memory, but on mathematics. I believe that with the correct mathematical approach and the use of a common algorithm, anyone with a basic mathematical mind can do this in their head.
Answered by Chris Fisher. 





A 3 by 3 block on a calendar 
20060118 

From A student: Choose two different blocks of nine numbers arranged 3 across and 3 down on a calendar, and check that this rule holds: For any block of nine numbers the average of the four corner numbers is equal to the middle number. Show your work and explain why the rule works. Answered by Penny Nom. 





When will the calendar be the same as 2002? 
20020220 

From John: When will the calendar be the same as 2002? I know the answer is 2013, but I don't know how to answer this mathematically, or if it is possible to do so. This is a ninth grade level algebra question my daughter received from her teacher. Any ideas? Answered by Chris Fisher, Patrick Maidorn and Penny Nom. 





Theme day 
20011014 

From A teacher: I woulld like a math theme for a theme day in a high school, grades 912. Our last theme was fractal fest. Answered by Penny Nom and Claude Tardif. 





The astronomers' calendar 
20001129 

From Show_Li: The calendar that astronomers use began on Jan. 1, 4713 B.C. on that day, the julian calendar, the lunar calendar, and roman tax system calendar all coincided. This won't happen again until 3267 A.D. (a). How many years ago was the astronomer's calendar started? (b). Find the number of years between times that the three calendars coincided. Answered by Penny Nom. 





Leap Year 
20000920 

From Jennifer: The earth revolves around the sun in 365.24 days. How does our calendar deals with the extra 0.24 day? Answered by Penny Nom. 

