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

Introduction / Context:
This question asks you to move one year backward from a known date and weekday. The twist is that 2004 was a leap year, which changes how many days the calendar shifts by for the same date in consecutive years.

Given Data / Assumptions:
• 6 March 2005 was a Monday.• We want to find the weekday on 6 March 2004.• 2004 is a leap year (divisible by 4 and not a century year).

Concept / Approach:
From one year to the next, the same calendar date usually shifts by 1 weekday for a normal year and by 2 weekdays for a leap year, but the position of 29 February matters. Since we are going backwards from 2005 to 2004, we must subtract the shift instead of adding.

Step-by-Step Reasoning:
Step 1: Consider moving from 6 March 2004 to 6 March 2005.Step 2: The interval includes 29 February 2004 (because that date lies before 6 March in a leap year).Step 3: Therefore, between 6 March 2004 and 6 March 2005, the calendar advances by 366 days, which is 2 days modulo 7.Step 4: So 6 March 2005 is 2 weekdays ahead of 6 March 2004.Step 5: We know 6 March 2005 is Monday. To go backwards one year, subtract 2 days from Monday.Step 6: Monday → Sunday (1 day back) → Saturday (2 days back).Step 7: Therefore, 6 March 2004 was a Saturday.

Verification:
If 6 March 2004 is Saturday, then adding 2 days (for the leap year shift) gives Monday, matching the given weekday for 6 March 2005. This confirms the reasoning.

Why Other Options Are Wrong:
Sunday, Tuesday, Wednesday: These would correspond to subtracting 1, 6, or 5 days from Monday instead of 2, which is not appropriate for a leap year where the date is after 29 February.

Common Pitfalls:
A frequent error is to treat every year as shifting the date by only 1 weekday, ignoring leap years. Another mistake is to forget that 6 March is after 29 February, so the extra leap day must be included in the count.

Final Answer:
6th March 2004 was a Saturday.