Calendar basics — Find the last day (weekday) of the year 2006. (Use Gregorian calendar rules; 2006 is not a leap year.)

Introduction / Context:
Determining the weekday for the last day of a year is a classic calendar arithmetic problem. We use the facts that a common (non-leap) year has 365 days (which is 52 weeks + 1 day), and a leap year has 366 days (52 weeks + 2 days). This shifts the weekday of the last day relative to the first day of the year.

Given Data / Assumptions:

• Year: 2006.
• Gregorian rules: a leap year is divisible by 4, except centuries must be divisible by 400.
• We need the weekday of December 31, 2006.

Concept / Approach:
In any common year (365 days), the weekday advances by +1 from January 1 to December 31. If we know January 1, 2006, then December 31, 2006 is the same weekday as January 1, 2006 (because there are 365 = 7 * 52 + 1 days, and the +1 shift from Jan 1 to Jan 2 accumulates so that Dec 31 matches Jan 1). Alternatively, recall (or compute) that January 1, 2006 was Sunday.

Step-by-Step Solution:

Verification / Alternative check:

Why Other Options Are Wrong:

Common Pitfalls:

Final Answer:
Sunday