If 1st January 2001 was Monday then what day of the week was it on 31st December 2001 ?
The Correct Answer and Explanation is:
If 1st January 2001 was a Monday, then 31st December 2001 was a Monday as well.
Explanation
To determine the day of the week on 31st December 2001, given that 1st January 2001 was a Monday, we need to count how many days have passed in the year and how that affects the weekday.
The key concept here is that the day of the week advances by one for every non-leap year (because 365 ÷ 7 = 52 weeks and 1 day). That one extra day causes the weekday to move forward by one day.
However, in this case, we are looking at the same calendar year — from 1st January 2001 to 31st December 2001 — so we will look at the total number of days between these two dates.
Step 1: Check if 2001 is a leap year
A year is a leap year if:
- It is divisible by 4, and
- Not divisible by 100, unless also divisible by 400.
2001 is not divisible by 4, so it is not a leap year. Therefore, it has 365 days.
Step 2: Count the number of days from 1st January to 31st December
From 1st January to 31st December is 365 days. Since we are calculating inclusive of 1st January (which was Monday), the 365th day will be the same day of the week as the first day, because:
- 365 ÷ 7 = 52 weeks + 1 day.
- That 1 extra day pushes the weekday forward by 1.
So, 1st January 2001 was a Monday. After 364 days (52 full weeks), we reach 30th December 2001, which would also be a Sunday. The next day, 31st December, is Monday.
Thus, 31st December 2001 was also a Monday. ✅
