Starting date: 1 January 2018 is a Monday
Ending date: 31 December 2020
To find the day of the week on 31 December 2020, calculate the total number of days from 1 January 2018 to 31 December 2020.
For 2018 (not a leap year): From 1 January to 31 December = 365 days
For 2019 (not a leap year): Full year = 365 days
For 2020 (leap year, divisible by 4): Full year = 366 days
Total days from 1 January 2018 to 31 December 2018 = 365 - 1 = 364 days (excluding the start date)
Total days from 1 January 2018 to 31 December 2019 = 364 + 365 = 729 days
Total days from 1 January 2018 to 31 December 2020 = 729 + 366 = 1095 days
To find the day of the week, divide the total days by 7:
1095÷7=156 remainder 3
This means 31 December 2020 is 3 days after Monday.
Monday + 3 days = Thursday
Therefore, 31 December 2020 was a Thursday.
The correct answer is Option 4: Thursday