Same date next year (leap-year shift): If January 3, 2008 was a Friday, what day of the week fell on January 3, 2009?

Introduction / Context:
When moving from a given calendar date to the same date in the next year, the weekday shift depends on whether the year in between is a leap year (366 days) or a common year (365 days). A 365-day span advances the weekday by 1; a 366-day span advances it by 2, because 365 ≡ 1 (mod 7) and 366 ≡ 2 (mod 7).

Given Data / Assumptions:

• January 3, 2008 = Friday.
• We need the weekday on January 3, 2009.
• Year 2008 is a leap year (divisible by 4 and also by 400 rule for centuries; 2008 qualifies by divisibility by 4 and is not a century year).

Concept / Approach:
If the span from one year’s date to the next passes through a leap year, the weekday advances by 2. Otherwise, it advances by 1. Here we cross the body of 2008 (a leap year).

Step-by-Step Solution:

Verification / Alternative check:
Enumerating two steps from Friday: Saturday (1), Sunday (2). Matches the modular reasoning.

Why Other Options Are Wrong:
Monday/Tuesday/Saturday correspond to +3/+4/ +1 steps, which do not match a leap-year span of +2.

Common Pitfalls:
Forgetting that leap years shift by two days for the same date next year, not one day.

Final Answer:
Sunday