On January 12, 1980 it was Saturday. What was the day of the week on January 12, 1979?

Introduction / Context:
Consecutive dates one year apart shift by +1 weekday if the year in between is a common year, and by +2 if it is a leap year and the date is on or after February 29.

Given Data / Assumptions:

• Jan 12, 1980 = Saturday.
• 1979 is a common year.

Concept / Approach:
From Jan 12, 1979 to Jan 12, 1980 spans a common year. Therefore the weekday advances by +1 day.

Step-by-Step Solution:
If Jan 12, 1979 was X, then Jan 12, 1980 was X + 1 day.Given Jan 12, 1980 = Saturday → X = Friday.

Verification / Alternative check:
Calendar tables confirm Friday for Jan 12, 1979.

Why Other Options Are Wrong:
Thursday or Sunday imply shifts inconsistent with a single common year difference.

Common Pitfalls:
Adding +2 because 1980 is a leap year; the leap offset matters when crossing Feb 29 from earlier in the year.

Final Answer:
Friday