In December 1991, it is given that 1 December 1991 is the first Sunday of the month. On which date in December 1991 does the fourth Tuesday occur?

Introduction / Context:
This is a straightforward calendar counting problem where you are told the weekday of the first day of a month, and you must determine the date corresponding to the fourth occurrence of another weekday in the same month. Such questions reinforce how weekdays repeat every seven days and train you to quickly jump by weekly intervals without drawing a full calendar every time.

Given Data / Assumptions:

• 1 December 1991 is a Sunday.
• We are asked for the date of the fourth Tuesday of December 1991.
• Each week has seven days and weekdays repeat regularly.
• We are working within December 1991 only, so there is no crossing into another month.

Concept / Approach:
Once we know that 1 December is a Sunday, we can determine the weekday for each subsequent date by adding one day at a time or by jumping in blocks of seven days. The first Tuesday will occur two days after Sunday, and each subsequent Tuesday will be seven days apart from the previous one. Therefore, listing the first, second, third, and fourth Tuesdays is a simple matter of adding 7 each time to the first Tuesday date.

Step-by-Step Solution:
Step 1: If 1 December is Sunday, then 2 December is Monday. Step 2: Therefore, 3 December is Tuesday. This is the first Tuesday of December 1991. Step 3: The second Tuesday will be 7 days after the first Tuesday, so it falls on 3 + 7 = 10 December. Step 4: The third Tuesday will be 7 days after the second, so it falls on 10 + 7 = 17 December. Step 5: The fourth Tuesday will be 7 days after the third, so it falls on 17 + 7 = 24 December. Step 6: Thus, the fourth Tuesday of December 1991 is 24.12.91.

Verification / Alternative check:
If you want to verify, you can mentally sketch the sequence of weekdays starting with Sunday on the first and write down the first few dates: 1 Sunday, 2 Monday, 3 Tuesday, 4 Wednesday, 5 Thursday, 6 Friday, 7 Saturday, 8 Sunday, and so on. Mark the Tuesdays you encounter. You will see that the four Tuesdays appear on the 3rd, 10th, 17th, and 24th of December. As long as you add exactly seven days between Tuesdays, you will end up at the same dates without any doubt.

Why Other Options Are Wrong:
17.12.91 corresponds to the third Tuesday, not the fourth. The date 27.12.91 is a Friday, so it does not correspond to any Tuesday at all. The date 31.12.91 is the fifth Tuesday only if weekday alignment allows, but in this month 31 December 1991 falls on a Tuesday after the fourth Tuesday has already occurred on the 24th. Therefore, among the given choices, only 24.12.91 is the correct fourth Tuesday.

Common Pitfalls:
Students often miscount by treating the first Tuesday as the second or by forgetting that the counting starts from the first occurrence of the weekday in the month. Another pitfall is to assume that the fourth Tuesday must fall close to the end of the month, which is not always true. It is safer to use the basic seven day jump method and list dates explicitly when you are still getting comfortable with calendar problems.

Final Answer:
So, the fourth Tuesday of December 1991 falls on 24.12.91.