On 8 December 2007, Saturday fell. Using this information, what day of the week was 8 December 2006 according to the Gregorian calendar?

Introduction / Context:
This question uses relative calendar reasoning rather than a specific formula. You are told the weekday for 8 December 2007 and asked to find the weekday for 8 December 2006. By understanding how weekdays shift from one year to the next, especially across leap and non leap years, you can answer quickly without recalculating from scratch.

Given Data / Assumptions:
- 8 December 2007 was a Saturday.
- We are working in the Gregorian calendar.
- We must determine the weekday on 8 December 2006.
- Years 2006 and 2007 are consecutive years.
- 2007 is not a leap year; 2006 is also not a leap year.

Concept / Approach:
Between the same calendar date in two consecutive non leap years, the weekday shifts by exactly one day. This is because a non leap year has 365 days, which is 52 weeks plus 1 day. Therefore, if you know the weekday for a date in 2007, then the same date in 2006 or 2008 can be found by shifting one weekday step backward or forward respectively.

Step-by-Step Solution:
Step 1: Note that 2007 is not a leap year (it is not divisible by 4).Step 2: A non leap year contributes a shift of 1 weekday between the same date in consecutive years.Step 3: 8 December 2007 is given as Saturday.Step 4: To find the weekday on 8 December 2006, we move one day backward, because we are going to the previous year.Step 5: One day before Saturday is Friday.Step 6: Therefore, 8 December 2006 was a Friday.

Verification / Alternative check:
You can also think in the forward direction: if 8 December 2006 were Friday, then adding one year of 365 days (which is 1 day extra beyond complete weeks) would shift the weekday forward to Saturday on 8 December 2007. This is consistent with the given information, so the backward reasoning is confirmed to be correct.

Why Other Options Are Wrong:
If you mistakenly think that the shift is 2 days, you might answer Thursday or Sunday, but neither appears in the options. Choosing Saturday would mean no shift at all, which is not possible for a full non leap year. Monday, Tuesday and Wednesday represent different, incorrect shifts and do not match the correct relationship between the two years.

Common Pitfalls:
Common errors include confusing leap year and non leap year shifts, or trying to count day by day across the entire year, which is time consuming and more error prone. Remember the key rule: 365 days cause a 1 day shift, 366 days cause a 2 day shift. Then, simply apply that rule in the correct direction when moving forward or backward between years.

Final Answer:
The day of the week on 8 December 2006 was Friday.