Q. If 6th March, 2005 is Sunday, what was the day of the week on 6th March, 2002?

Explanation by: Mr. Dubey

Number of odd days between 6th march 2002 to 6th march 2003 is 1
Number of odd days between 6th march 2003 to 6th march 2004 is 2
Number of odd days between 6th march 2004 to 6th march 2005 is 1
Hence total Number of odd days between 6th march 2002 to 6th march 2005 is 1 + 2 + 1 = 4 odd days so 6th march 2002 is 4 days before Sunday i.e. Wednesday.