What day of the week was 1st January 2100?

medium Q8 of 15

Reasoning Ability - Calendar Problems

AFriday

BSaturday

CSunday

DMonday

Step-by-Step Solution

Step 1: Jan treated as month 13 of previous year
For Zeller’s Rule use q = 1, m = 13, year = 2099.
Step 2: Compute K and J
K = 2099 % 100 = 99, J = floor(2099 / 100) = 20.
Step 3: Evaluate components
floor(13*(13+1)/5) = 36;
floor(K/4)=24;
floor(J/4)=5;
5*J = 100.
Total: h = (1 + 36 + 99 + 24 + 5 + 100) = 265 → 265 mod 7 = 6.
Step 4: Map result to weekday
Zeller mapping: 0 = Saturday, 1 = Sunday, 2 = Monday, 3 = Tuesday, 4 = Wednesday, 5 = Thursday, 6 = Friday. So h = 6 → Friday.
Final Answer:
Friday → Option A
Quick Check:
Alternate check from 1-Jan-2000 (Saturday) + odd days for 100 years (125 ≡ 6) → Saturday + 6 = Friday ✅

Quick Trick: Century years not divisible by 400 are ordinary; use Zeller with Jan as month 13 of previous year.

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