Final answer:
Since 2020 was a leap year with 366 days, and 366 days comprise 52 weeks plus 2 days, the day of the week advances by 2 days from January 1st. Thus, if January 1, 2020, was a Tuesday, then December 31, 2020, was a Thursday.
Step-by-step explanation:
If January 1, 2020 was a Tuesday, we can determine the day of the week for December 31, 2020 by counting the number of days in the year 2020 and seeing how many days that would shift the day of the week from January 1st.
Since 2020 was a leap year, it had 366 days. The number of weeks in 366 days is 366 divided by 7, which gives us 52 weeks with 2 days leftover. Therefore, the day of the week will advance by 2 days from Tuesday. Counting forward, after Tuesday comes Wednesday, and then Thursday.
To determine the day of the week on December 31, 2020, we need to count the number of days between January 1, 2020, and December 31, 2020. There are 365 days in a non-leap year. Since January 1, 2020, was a Tuesday, we can start counting from that day.
Using modulo arithmetic, we can find the remainder when dividing the total number of days by 7. This remainder will tell us the day of the week. Counting 365 days from a Tuesday, we find that December 31, 2020, will fall on a Thursday (option d).
Therefore, the correct answer is option d. Thursday.