Relating known weekday to a prior year: If March 6, 2005 was a Monday, what was the day of the week on March 7, 2004?

Introduction / Context:
Relating weekdays across years demands careful handling of leap days. Here, we are given a weekday in 2005 and asked for a weekday in 2004. The key idea is to use the same calendar date one year apart (March 7, 2004 ↔ March 7, 2005) and the fact that between those dates there are 365 days (not 366), since Feb 29, 2004 lies before March 7, 2004 and is therefore not traversed in that one-year span.

Given Data / Assumptions:

• March 6, 2005 = Monday.
• We want March 7, 2004.
• From March 7, 2004 to March 7, 2005 is 365 days ⇒ +1 weekday.

Concept / Approach:
First find March 7, 2005 from March 6, 2005, then step back one year to March 7, 2004 by subtracting one weekday (the inverse of +1).

Step-by-Step Solution:

Verification / Alternative check:
Directly: Mar 7, 2004 + 365 days = Mar 7, 2005. So the weekday must advance by +1; reversing gives Monday.

Why Other Options Are Wrong:
Tuesday/Friday/Sunday correspond to different offsets (0, ±2, etc.) that do not match the 365-day relationship used here.

Common Pitfalls:
Assuming +2 because 2004 is a leap year; the extra day does not lie within Mar 7, 2004 → Mar 7, 2005.

Final Answer:
Monday