Stage: 2 Challenge Level: 
How often do leap years occur?
What day of the week was the 1st January 2001 ... 1st January 2002 etc.?
What happens after $28$ years?
What day of the week was the 1st January 2001 ... 1st January 2002 etc.?
What happens after $28$ years?
Factors and multiples. Investigations. Speed. Time. Addition & subtraction. Generalising. Calendars. Sequences. Length/distance. Clock.
Published October 2000.
Copyright © 2007. University of Cambridge. All rights reserved.
NRICH is part of the family of activities in the Millennium Mathematics Project, which also includes the Plus and Motivate sites.
email: nrich@damtp.cam.ac.uk