On 8th December 2007, it was a Saturday. What day of the week was it on 8th December 2006?

Introduction / Context:
This question asks you to move one year backward from a given date and weekday. The key is to know how many days the calendar shifts in one year, and whether that year is a leap year or not.

Given Data / Assumptions:
• 8 December 2007 was a Saturday.• We want the weekday on 8 December 2006.• 2007 is not a leap year.

Concept / Approach:
From a date in one year to the same date in the next year, the weekday advances by 1 day in a normal year (365 days ≡ 1 mod 7), and by 2 days in a leap year (366 days ≡ 2 mod 7). Here we move from 8 December 2006 to 8 December 2007 across 2007, which is a non-leap year.

Step-by-Step Solution:
Step 1: The period from 8 December 2006 to 8 December 2007 spans exactly 365 days, since 2007 is a normal year and the dates are one year apart.Step 2: 365 days correspond to 1 extra day of the week (because 365 mod 7 = 1).Step 3: Therefore, 8 December 2007 is 1 weekday ahead of 8 December 2006.Step 4: We know 8 December 2007 is Saturday.Step 5: To go back to 8 December 2006, subtract 1 day: Saturday → Friday.Step 6: Thus, 8 December 2006 was a Friday.

Verification:
If 8 December 2006 is Friday, then adding 1 day (for the normal year shift) gives Saturday on 8 December 2007, which matches the given information.

Why Other Options Are Wrong:
Saturday: Would imply no shift in weekday, which is impossible over a full non-leap year.Monday or Tuesday: These would correspond to going back by more than 1 day, which does not match the one-day shift for a normal year.

Common Pitfalls:
Candidates sometimes mistakenly treat any year as contributing 2 days of shift or forget to check whether the year is a leap year. Another error is moving in the wrong direction (adding instead of subtracting when going to the previous year).

Final Answer:
On 8th December 2006, it was a Friday.