It is given that 1.12.91 (1 December 1991) is the first Sunday of the month.\nWhich date is the fourth Tuesday of December 1991?

Introduction / Context:
This calendar question focuses on finding the date of a specific weekday occurrence within a month. You are told that 1 December 1991 is the first Sunday of the month, and you are asked to find which date is the fourth Tuesday. The process involves listing weekdays sequentially and tracking Tuesdays in particular.

Given Data / Assumptions:

1 December 1991 is a Sunday, and it is the first Sunday in that month.

We need the date of the 4th Tuesday in December 1991.

The week pattern is Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, then repeats.

Concept / Approach:
Start from the known weekday (1 December is Sunday) and build the weekday calendar for the first several days of December. Identify the first Tuesday, then add 7 days each time to reach the second, third, and finally the fourth Tuesday. Every nth Tuesday is exactly 7*(n-1) days after the first Tuesday.

Step-by-Step Solution:
Step 1: List the weekdays for the first few days of December 1991. 1 Dec: Sunday. 2 Dec: Monday. 3 Dec: Tuesday → 1st Tuesday. 4 Dec: Wednesday. 5 Dec: Thursday. 6 Dec: Friday. 7 Dec: Saturday. Step 2: Use the 7-day repetition for Tuesdays. 2nd Tuesday = 3 + 7 = 10 December. 3rd Tuesday = 10 + 7 = 17 December. 4th Tuesday = 17 + 7 = 24 December. Therefore, the fourth Tuesday falls on 24.12.91.

Verification / Alternative check:
You can verify by writing out Tuesdays explicitly: 3rd, 10th, 17th, and 24th are Tuesdays. The next Tuesday would be 31st, which would be the fifth Tuesday. Since the question specifically asks for the fourth Tuesday, 24 December is correct.

Why Other Options Are Wrong:
17.12.91 is the third Tuesday, not the fourth. 27.12.91 is a Friday based on the pattern, and 31.12.91 would be a Tuesday but it is the fifth Tuesday, not the fourth. Therefore, none of these match the required occurrence.

Common Pitfalls:
One common error is miscounting the first Tuesday, sometimes assuming it starts on the 2nd instead of the 3rd. Another is forgetting that Tuesday repeats every 7 days and instead counting incorrectly. Keeping a simple day-by-day list for the first couple of weeks helps ensure that you correctly identify each occurrence of Tuesday.

Final Answer:
The fourth Tuesday of December 1991 is on 24.12.91.