If 27th February 2011 was a Sunday, then, according to the Gregorian calendar, on which day of the week did 1st March 2012 fall?

Introduction / Context:
This calendar problem spans more than one year and involves a leap year. You are given that 27th February 2011 is a Sunday and asked to find the weekday for 1st March 2012. To solve it, you must carefully count the days between the two dates, taking into account that 2012 is a leap year and contains a 29th February.

Given Data / Assumptions:

• 27th February 2011 is a Sunday (given).
• We need the weekday on 1st March 2012.
• 2011 is a non-leap year with 365 days (no 29th February).
• 2012 is a leap year with 366 days (it has a 29th February).
• We assume the standard Gregorian calendar.

Concept / Approach:
We can break the interval from 27th February 2011 to 1st March 2012 into two parts:

• From 27th February 2011 to 27th February 2012.
• From 27th February 2012 to 1st March 2012.

We find the weekday shift for each part separately and then combine them. The key point is that the year 2012 is a leap year, so its February has 29 days, which slightly alters the number of days between the two dates.

Step-by-Step Solution:
Step 1: From 27th February 2011 (Sunday) to 27th February 2012 is exactly one year. Step 2: The year that we cross is 2011, which is a non-leap year with 365 days. Step 3: 365 days correspond to 52 weeks and 1 day, so the weekday advances by 1 day. Step 4: Therefore, 27th February 2012 is one day after Sunday, i.e., Monday. Step 5: Now consider the period from 27th February 2012 (Monday) to 1st March 2012. Step 6: In 2012 (a leap year), February has 29 days, so after 27th February comes 28th February, then 29th February, then 1st March. Step 7: Count the days from 27th February 2012 to 1st March 2012: From 27th to 28th: 1 day; 28th to 29th: another day; 29th to 1st March: another day. Total = 3 days. Step 8: Starting at Monday (27th February 2012), move forward 3 days: Tuesday (1), Wednesday (2), Thursday (3). Step 9: Therefore, 1st March 2012 falls on a Thursday.

Verification / Alternative check:
You can also verify this answer by using known calendar facts: standard tables for 2012 show that 1st March 2012 is indeed a Thursday. Computing the total days from 27th February 2011 to 1st March 2012 and then reducing modulo 7 also leads to a shift of 4 weekdays overall (Sunday → Thursday), consistent with the step-by-step decomposition above.

Why Other Options Are Wrong:
Friday, Sunday, Monday or Tuesday would require different net shifts (5, 0, 1 or 2 days) from the original Sunday, which are not supported by the actual day counts across 2011 and February 2012. Only a 4-day net shift, yielding Thursday, fits the true number of days in this interval.

Common Pitfalls:
The most common mistake is forgetting that 2012 is a leap year and therefore includes a 29th February, which adds an extra day between late February and March. Another pitfall is confusing which year (2011 or 2012) determines the one-day weekday shift when going from a date in one year to the same date in the next. Keeping the interval split and handling each part carefully helps avoid errors.

Final Answer:
1st March 2012 fell on Thursday.