Century boundaries — If the 1st day of a century is Thursday, the 1st day of the next century must be which weekday?

Introduction / Context:
Weekday shifts over 100 years differ depending on whether the century year at the end of the block is a leap year (divisible by 400) or not. This dictates what the next century's first day can be.

Given Data / Assumptions:

• Current century starts on Thursday.
• Next century begins 100 years later.
• Only years divisible by 400 are leap years among the centuries.

Concept / Approach:
Over a 100-year span, the weekday advances by +5 if the closing century is not a 400-multiple; if it is a 400-multiple, the net shift is +6 (one extra leap day). Starting from Thursday, +5 → Tuesday; +6 → Wednesday.

Step-by-Step Solution:

Verification / Alternative check:
Historical patterns of 1700→1800 and 1600→1700 illustrate the +5 vs +6 behavior.

Why Other Options Are Wrong:

• Other pairs do not correspond to the possible +5/+6 shifts from Thursday.

Common Pitfalls:

• Treating every century as leap; only 400-multiples are.

Final Answer:
Tuesday or Wednesday