In the month of April 2001, on which dates did Wednesday fall according to the Gregorian calendar?

Introduction / Context:
This question focuses on identifying all the dates in a particular month that fall on a specific weekday. Here, we are looking at April 2001 and trying to determine on which dates Wednesday occurred. Problems of this type test your ability to work with the structure of a month once you know the weekday of one of its dates or of a nearby date.

Given Data / Assumptions:
- Month and year: April 2001.
- We want all dates in April 2001 that are Wednesdays.
- We are using the standard Gregorian calendar.
- We assume that the day-of-week pattern within a month repeats every 7 days (as usual).

Concept / Approach:
Once you know the weekday of any one date in the month, every seventh day from that date will fall on the same weekday. Thus, if you find, for example, that 4 April 2001 is a Wednesday, then 11, 18 and 25 April 2001 must also be Wednesdays. The main task is to correctly identify the weekday of a single date in April 2001 and then extend the pattern.

Step-by-Step Solution:
Step 1: Use a known reference such as 1 January 2001 and determine its weekday if needed, then count forward to early April 2001.Step 2: Through standard calendar calculations, you find that 4 April 2001 was a Wednesday.Step 3: Once this is known, add 7 days repeatedly to generate the remaining Wednesdays in April.Step 4: 4 + 7 = 11, so 11 April 2001 is also a Wednesday.Step 5: 11 + 7 = 18, so 18 April 2001 is again a Wednesday.Step 6: 18 + 7 = 25, giving 25 April 2001 as the next Wednesday.Step 7: Adding another 7 would give 32, which is beyond the last date of April, so we stop here.

Verification / Alternative check:
You can verify by checking that 1 April 2001 was a Sunday (a fact from standard calendars), and then counting forward: 2 April Monday, 3 April Tuesday, 4 April Wednesday. This confirms that 4 April is indeed a Wednesday. From there, stepping forward in increments of 7 days gives 11, 18 and 25 as Wednesdays. All other dates in April either fall on different weekdays or are not valid dates for this month.

Why Other Options Are Wrong:
The sets 2nd, 9th, 16th, 23rd or 1st, 8th, 15th, 22nd correspond to sequences spaced 7 days apart but starting from the wrong initial weekday. The other listed combinations include dates that are not Wednesdays in April 2001 or contain incorrect starting points. Only 4th, 11th, 18th, 25th consistently match the Wednesday pattern for that month and year.

Common Pitfalls:
Students sometimes assume that the 1st of any month is a Monday or that months always start on the same weekday from year to year, which is not correct. Another common error is miscounting when adding 7 repeatedly. To avoid these issues, always anchor your counting to a correctly determined weekday and then proceed systematically in steps of 7 days.

Final Answer:
In April 2001, Wednesdays fell on 4th, 11th, 18th and 25th.