If 12 February 1986 falls on a Wednesday, then on which day of the week does 1 January 1987 fall in the Gregorian calendar?

Introduction / Context:
This question uses relative date reasoning within and across years. Instead of giving you the weekday for 1 January directly, it provides the weekday for 12 February 1986 and asks for the weekday of 1 January 1987. You must carefully track how many days lie between these two dates and how calendar rules for leap and non leap years affect the weekday shift.

Given Data / Assumptions:
- 12 February 1986 is a Wednesday.
- We want the weekday on 1 January 1987.
- Calendar: Gregorian calendar.
- 1986 is not a leap year (it is not divisible by 4).
- We must move from 12 February 1986 through the rest of 1986 and into 1987.

Concept / Approach:
We can count the number of days from 12 February 1986 to 1 January 1987, reduce that count modulo 7, and then shift the weekday accordingly. Since 1986 is a non leap year, it has 365 days. The key is to count how many days remain in 1986 after 12 February and then see how that affects the weekday when we arrive at 1 January 1987.

Step-by-Step Solution:
Step 1: Because 1986 is a non leap year, February has 28 days.Step 2: From 12 February to 28 February there are 16 days (days 13 to 28 inclusive).Step 3: From March to December 1986, sum the days in each month: March 31, April 30, May 31, June 30, July 31, August 31, September 30, October 31, November 30, December 31.Step 4: That sum is 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30 + 31 = 306 days.Step 5: Total days from 13 February 1986 to 31 December 1986 are 16 + 306 = 322 days, so from 12 February 1986 (inclusive step) to 1 January 1987 we advance 323 days.Step 6: Compute 323 modulo 7. Since 7 * 46 = 322, the remainder is 1.Step 7: A remainder of 1 means the weekday advances by 1 day from Wednesday.Step 8: One day after Wednesday is Thursday, so 1 January 1987 falls on a Thursday.

Verification / Alternative check:
You can cross check by noting that a full non leap year shifts a date by one weekday. If you could find the weekday of 1 January 1986 relative to 12 February 1986, you would see that going from the start of 1986 to the start of 1987 involves a one day forward shift, consistent with the remainder 1 obtained in the calculation above.

Why Other Options Are Wrong:
If you mistakenly computed the remainder as 0, you might pick Wednesday (no shift). If you miscount and get 2 or more as the remainder, you could be tempted by Friday or Monday. However, accurate counting of days and proper modulo 7 arithmetic leads to a shift of exactly one day, which matches Thursday only.

Common Pitfalls:
Students sometimes miscount the remaining days in February or forget whether to include the starting day when computing total days. Another common error is to treat 1986 as a leap year and give February 29 days, which would add an extra day and change the remainder. Double check month lengths and leap year status before summing.

Final Answer:
Under the given assumption, 1 January 1987 falls on a Thursday.