If 17 March 1997 was a Monday, what day of the week was 17 March 1996, using standard leap-year and weekday-shift rules?

Introduction:
This problem asks us to find the day of the week for a specific date one year earlier, given the weekday for the same calendar date one year later. It involves recognising that the type of year (leap or non-leap) and whether the 29 February falls in between are important factors in calculating the weekday shift.

Given Data / Assumptions:
17 March 1997 is Monday. We must find the weekday on 17 March 1996. We use standard leap-year rules. 1996 is divisible by 4, so 1996 is a leap year.

Concept / Approach:
The day of the week advances by 1 day after a non-leap year (365 days = 52 weeks + 1 day) and by 2 days after a leap year (366 days = 52 weeks + 2 days). Here we are moving backwards in time from 17 March 1997 to 17 March 1996. The year 1996 is a leap year, and the date 17 March is after 29 February, so the full leap-year shift must be taken into account.

Step-by-Step Solution:
Step 1: Understand the relationship between the dates. We move from 17 March 1996 to 17 March 1997: this interval includes the entire leap year 1996 and part of 1997, but for weekday purposes, we focus on the full-year shift from the date to the same date next year. Step 2: Identify year type. 1996 is a leap year (divisible by 4 and not a century year). For dates after 29 February, the same date in the next year is shifted by 2 weekdays compared with the previous year. Step 3: Apply the weekday shift. Let D1996 be the weekday on 17 March 1996. Then 17 March 1997, being one year after 17 March 1996 in a leap-year context (after 29 February), will be D1996 + 2 days. We are given that 17 March 1997 is Monday. So D1996 + 2 = Monday. Therefore, D1996 = Monday − 2 days. Counting backwards: Monday → Sunday (−1) → Saturday (−2). So 17 March 1996 was a Saturday.

Verification / Alternative check:
We can explicitly trace the sequence just around those dates. Since 1996 is a leap year with 29 February, and 17 March occurs after the extra day, the shift from 17 March 1996 to 17 March 1997 must be 2 days forward. Thus, if 1996 had Saturday, 1997 has Monday, which matches the given information.

Why Other Options Are Wrong:
Monday: This would imply a shift of 0 days, which is impossible across a full year. Tuesday or Wednesday: These correspond to incorrect backward shifts (−6, −5, or similar), not the required 2-day backward difference. Sunday: This would mean only a 1-day shift instead of 2, ignoring the leap-year effect.

Common Pitfalls:
Many learners forget that leap years cause a 2-day shift only for dates after 29 February. Others may mistakenly apply only a 1-day shift between the same dates in consecutive years, regardless of leap-year status. Always check whether the date is before or after 29 February in the leap year.

Final Answer:
The day of the week on 17 March 1996 was Saturday.