What was the day of the week, 15 August 2013?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Thursday
The weekday repeats every 7 days, so only the odd days, the days left over after whole weeks, decide it. Counting the odd days from the start of the era up to 15 August 2013, with 0 odd days = Sunday, 1 = Monday and so on:
The complete years 1 to 2012:
2000 years: 0 odd days (every 400 years has a whole number of weeks)
2001 to 2012: 12 years with 3 leap years (2004, 2008, 2012), so \(12+3=15\) odd days = 2 weeks + 1 odd day
From 1 January to 15 August 2013 (odd days of each month):
January 3, February 0 (28 days), March 3, April 2, May 3, June 2, July 3, August (15 days) 1
Total: \(3+0+3+2+3+2+3+1=17\) = 2 weeks + 3 odd days
Together:
\(1+3=4\) odd days, and 4 stands for Thursday
Tip: The month counts 3, 0, 3, 2, 3, 2, 3, 3, 2, 3, 2, 3 (January to December, ordinary year) are worth memorising; in a leap year February gives 1 instead of 0.