If 6 March 2005 was a Monday, what was the day of the week on 6 March 2004?

Introduction / Context:
This question asks you to find the day of the week exactly one year earlier than a given date. You are told that 6 March 2005 was a Monday and must determine the weekday on 6 March 2004. It checks whether you understand how leap years affect the shift in weekdays from one year to the next.

Given Data / Assumptions:

• 6 March 2005 was a Monday.
• We want the day on 6 March 2004.
• 2004 is a leap year because it is divisible by 4 and the Gregorian rules treat it as leap.
• 6 March is after 29 February in a leap year.

Concept / Approach:
The weekday shift between two identical dates in consecutive years depends on whether the year in between is a leap year and on the position of the date relative to 29 February. For dates after 29 February in the leap year, the difference from that date to the same date in the next year is 365 days, giving 1 odd day. That means the weekday changes by one day between 6 March 2004 and 6 March 2005.

Step-by-Step Solution:
Step 1: Recognise that 2004 is a leap year and has 366 days. Step 2: However, when you go from 6 March 2004 to 6 March 2005, you do not include 29 February 2004 inside that interval, because it lies before 6 March 2004. Step 3: Therefore, the interval from 6 March 2004 to 6 March 2005 effectively covers 365 days. Step 4: 365 days correspond to 1 odd day, because 365 = 7 * 52 + 1. Step 5: This means that when moving forward from 6 March 2004 to 6 March 2005, the weekday advances by one day. Step 6: We are given that 6 March 2005 is Monday, so 6 March 2004 must be one day earlier, which is Sunday.

Verification / Alternative check:
You can verify this idea with a simpler example. If 15 April 2003 is a Wednesday and 2003 is a normal year, then 15 April 2004 would be Thursday because of one odd day. Moving backward from Thursday will again give Wednesday. Applying the same logic here, Monday one year later corresponds to Sunday one year earlier, confirming the answer.

Why Other Options Are Wrong:
Tuesday: This would require two odd days between the dates, which is not the case.

Wednesday: This would correspond to three odd days difference, again incorrect.

Friday: This weekday is too far from Monday for a simple one year shift where only one odd day is present.

Common Pitfalls:
Many students think that a leap year always produces two odd days between the same dates of consecutive years. This is only true when the period includes 29 February. Because our interval starts after 29 February 2004, only 365 days lie between the two dates. Always consider whether the leap day itself is part of the interval before deciding how many odd days to use.

Final Answer:
Thus, the day of the week on 6 March 2004 was Sunday.