Weekday across a leap year boundary: If March 5, 1999 was Friday, what day of the week was March 9, 2000?

Introduction / Context:
Weekday movement over a year depends on whether the interval covers a leap day (Feb 29). From a date in 1999 to the same date in 2000, we cross Feb 29, 2000 because 2000 is a leap year (divisible by 400). Hence the weekday advances by 2 for exactly one year, plus any extra days beyond that “same-date” point.

Given Data / Assumptions:

• March 5, 1999 = Friday.
• Find weekday on March 9, 2000.
• 2000 is a leap year under Gregorian rules.

Concept / Approach:
First move to March 5, 2000 (same calendar date): advance by +2 (leap span). Then move four more days to March 9, 2000. Total shift = +2 + 4 = +6 weekdays.

Step-by-Step Solution:

Verification / Alternative check:
Counting forward: Sun (Mar 5), Mon (6), Tue (7), Wed (8), Thu (9).

Why Other Options Are Wrong:
Wednesday/Saturday/Friday correspond to +5/+1/0 moves, inconsistent with +6.

Common Pitfalls:
Applying a +1 shift for the “year later” step despite crossing a leap day.

Final Answer:
Thursday