If 10th May 2013 was a Friday, what was the day of the week on 18th September 2015?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Friday
Only the odd days (days left over after whole weeks) move the day of the week. A year from one date to the same date gives 1 odd day, or 2 when a 29th February falls in between. So first move to 10th May 2015, then count the days to 18th September.
10 May 2013 to 10 May 2014: 365 days, 1 odd day
10 May 2014 to 10 May 2015: 365 days, 1 odd day (29th February 2016 comes later)
So 10 May 2015 was Friday + 2 = Sunday
Days after 10 May 2015 up to 18 September: \(21+30+31+31+18=131\) (rest of May, June, July, August, September)
\(131=18\times7+5\), so 5 odd days
Sunday + 5 = Friday