Hundred-year shift — If 1 January of year x is Monday, what is the first day of year x + 100?
Aptitude
Calendar
Difficulty: Easy
Choose an option
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AFriday
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BFriday or Saturday
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CSaturday or Sunday
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DNone of these
Answer
Correct Answer: Saturday or Sunday
Explanation
Introduction / Context:Advancing exactly 100 years changes the weekday by +5 (ordinary block) or +6 (if the terminal century year is a 400-multiple). We apply this to a Monday start.
Given Data / Assumptions:
- Year x starts on Monday (1 Jan).
- We seek the start day of year x+100.
Concept / Approach:From Monday, add +5 → Saturday (non-400 century) or +6 → Sunday (400-multiple). Thus two possibilities exist.
Step-by-Step Solution:
1) Determine whether the 100-year block ends at a 400-multiple year or not.2) Map the weekday shift accordingly: +5 or +6.3) Monday + 5 = Saturday; Monday + 6 = Sunday.Verification / Alternative check:Cross-check with known sequences around 1900/2000 to see Saturday/Sunday outcomes.
Why Other Options Are Wrong:
- Friday/Friday or Saturday do not match the +5/+6 mapping from Monday.
Common Pitfalls:
- Assuming a single unique weekday when two are possible.
Final Answer:Saturday or Sunday