Reasoning Ability - Calendar Problems
What day of the week was 31st December 1999?
What day of the week was 31st December 1999?
medium Q15 of 15
Step-by-Step Solution
Step 1: Month > 2 (no adjustment)
q = 31, m = 12, year = 1999.Step 2: Compute K and J
K = 99,J = 19.Step 3: Evaluate formula pieces
floor(13*(12+1)/5)=33;floor(K/4)=24;floor(J/4)=4;5J=95.
Sum:h = (31 + 33 + 99 + 24 + 4 + 95) = 286→286 mod 7 = 6.Step 4: Map to weekday
Zeller mapping:6 → Friday. So 31 Dec 1999 = Friday.Final Answer:
Friday → Option AQuick Check:
Day before 1 Jan 2000 (Saturday) is Friday ✅
Quick Trick: After computing h, map Zeller's index carefully (0=Sat,…,6=Fri) and cross-check adjacent known dates.
Common Mistakes:
MISTAKES- Reading h directly as conventional weekday without applying the mapping.
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