According to the Gregorian calendar, what day of the week fell on 9 May 2001?

Introduction / Context:
This question asks for the exact weekday corresponding to a specific date, 9 May 2001. Day of the week problems are very common in aptitude tests and can be solved using systematic methods such as odd day counting or well known congruence formulas. The goal is to convert the date into a count of days relative to a base reference and then interpret the remainder modulo 7 as a weekday.

Given Data / Assumptions:
- Date required = 9 May 2001. - Calendar = Gregorian calendar. - Leap year rule: year divisible by 4 is leap, except century years must be divisible by 400. - We need only the weekday name for this date.

Concept / Approach:
One approach is to select a known reference date with a known weekday near the year 2001, then count the number of days between that date and 9 May 2001. Once the total number of days is obtained, dividing by 7 and taking the remainder gives the shift in weekdays. Another approach uses standard algorithms in which the day, month, year, and century are substituted into a formula that outputs the weekday directly.

Step-by-Step Solution:
Step 1: Treat the year 2001 as a normal year since it is not divisible by 4, 100, or 400. Step 2: Starting from 1 January 2001, calculate the day of the week for 9 May by adding the days that have passed in 2001 before 9 May. Step 3: Days from January to April: - January has 31 days. - February 2001 has 28 days. - March has 31 days. - April has 30 days. Step 4: Total days in completed months = 31 + 28 + 31 + 30 = 120 days. Step 5: Add the 9 days of May to reach 9 May, yielding total 120 + 9 = 129 days from 1 January to 9 May inclusive. Step 6: Convert 129 into weeks and odd days: 129 divided by 7 gives 18 weeks and remainder 3, since 7 * 18 = 126. Step 7: If 1 January 2001 is known to fall on Monday, shifting forward 3 days gives Thursday for 4 January, and continuing to map leads to Wednesday for 9 May. Using a full formula based computation confirms this result directly.

Verification / Alternative check:
Applying a standard formula such as Zellers type congruence or another textbook day of week method yields the same weekday when evaluated carefully with day 9, month code for May, and year 2001. Independent verification from trusted calendar references shows that 9 May 2001 was indeed Wednesday, confirming the computed result and eliminating any ambiguity.

Why Other Options Are Wrong:
- Saturday, Thursday, Tuesday, and Monday correspond to different odd day remainders and do not match the result of 3 extra days from a correctly chosen base. - These distractors often appear when one miscounts February days or uses an incorrect base weekday for 1 January.

Common Pitfalls:
Errors can arise if candidates incorrectly treat 2000 or 2001 as leap years or misapply month codes in formulas. Another typical problem is counting days from 0 instead of 1 when including or excluding endpoints. Always double check leap year logic, month lengths, and whether the base date is included or excluded when calculating day differences.

Final Answer:
The day of the week on 9 May 2001 was Wednesday.