What was the day of the week on 1st January 2005?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Saturday
The weekday repeats every 7 days, so only the odd days, the days left over after whole weeks, decide it. An ordinary year has 1 odd day and a leap year 2, and every 400 years have 0 odd days. Counting from day 0 = Sunday, the total number of odd days gives the weekday.
The first 2000 years (to 31 December 2000) are five blocks of 400 years: 0 odd days
2001, 2002 and 2003 are ordinary years: 3 odd days
2004 is a leap year: 2 odd days
1 January 2005: 1 odd day
Total \(=0+3+2+1=6\) odd days, and day 6 is Saturday