Century starts — Which weekdays can a century year (…00) NOT start on?
Aptitude
Calendar
Difficulty: Medium
Choose an option
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AWednesday, Friday, and Sunady
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BWednesday, Friday, and Saturday
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CWednesday, Thursday, and Sunday
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DNone of these
Answer
Correct Answer: None of these
Explanation
Introduction / Context:Not all weekdays are possible for 1 January of a century year. Under Gregorian rules, century starts occur only on a subset of weekdays.
Given Data / Assumptions:
- Consider years …, 1700, 1800, 1900, 2000, 2100, …
- We examine which weekdays are attainable on 1 January of those years.
Concept / Approach:Empirical (and theoretical) analysis shows that century years start only on Monday, Wednesday, Friday, or Saturday.
Step-by-Step Solution:
1) Known examples: 1900 began on Monday; 2000 on Saturday; 2100 on Friday; 1800 on Wednesday.2) Therefore, the possible set is {Monday, Wednesday, Friday, Saturday}.3) The complements (Tuesday, Thursday, Sunday) are not possible.Verification / Alternative check:Apply 100-year weekday shifts (+5, +6) and cycle through samples to see the attainable set.
Why Other Options Are Wrong:
- Options A–C include weekdays that actually can occur (e.g., Wednesday, Friday, Saturday). Hence none of those groupings are correct.
Common Pitfalls:
- Mistyping “Sunday” as “Sunady.”
- Assuming any weekday is possible.
Final Answer:None of these