It is given that 1.12.91 (1 December 1991) falls on a Tuesday and this is the first Tuesday of the month.\nWhich date is the fourth Thursday of December 1991?

Introduction / Context:
Date-and-day questions often ask you to find the weekday or date of a specific repetition, such as the 3rd Monday or 4th Thursday in a month. In this problem, you are told that 1 December 1991 is a Tuesday, and you must find which date is the fourth Thursday of that same month.

Given Data / Assumptions:

1 December 1991 is a Tuesday.
We want the date of the 4th Thursday in December 1991.
Each week repeats the sequence of weekdays after 7 days.
The month of December has 31 days, but we mainly need its first few weeks.

Concept / Approach:
Start from the known weekday (1 December is Tuesday) and list out the weekdays for subsequent dates. Identify the first Thursday, then add 7-day intervals to find the 2nd, 3rd and 4th Thursdays. Because the weekly pattern repeats every 7 days, every nth Thursday is exactly 7*(n-1) days after the first Thursday.

Step-by-Step Solution:
Step 1: List the first few days of December 1991. 1 Dec: Tuesday 2 Dec: Wednesday 3 Dec: Thursday (this is the 1st Thursday). Step 2: Use the 7-day repetition to find subsequent Thursdays. 2nd Thursday = 3 + 7 = 10 December. 3rd Thursday = 10 + 7 = 17 December. 4th Thursday = 17 + 7 = 24 December. Thus, the fourth Thursday falls on 24.12.91.

Verification / Alternative check:
We can cross-check by listing the weekdays around 24 December. From 1 December (Tuesday), we get: 8 December (Tuesday), 15 December (Tuesday), 22 December (Tuesday). Therefore, 5 December is Thursday +2 days (Saturday), 12 December is Thursday +2 days, and so on. Counting properly, you will see that 24 December aligns with the fourth occurrence of Thursday.

Why Other Options Are Wrong:
22.12.91 and 23.12.91, based on the pattern, fall earlier in the week and do not correspond to a Thursday when 1 December is Tuesday.
25.12.91 is the Thursday after 24.12.91 only if the pattern were shifted, but with 1 December fixed as Tuesday, 25 December becomes a Wednesday, not Thursday.

Common Pitfalls:
Students sometimes mistakenly take 1 December as the first Thursday itself or forget to count the first occurrence properly, leading them to pick the 3rd or 5th Thursday instead. Keeping a small table of dates and weekdays or using the idea that each same weekday recurs after every 7 days helps avoid confusion.

Final Answer:
The fourth Thursday of December 1991 falls on 24.12.91.