What day of the week was 1st January 2010?

easy Q13 of 15

Reasoning Ability - Calendar Problems

AThursday

BSaturday

CFriday

DSunday

Step-by-Step Solution

Step 1: Adjust for January
Use q = 1, m = 13, year = 2009 (Jan treated as month 13 of previous year).
Step 2: Compute K and J
K = 2009 % 100 = 9, J = floor(2009/100) = 20.
Step 3: Evaluate components
floor(13*(m+1)/5) = 36;
floor(K/4)=floor(9/4)=2;
floor(J/4)=floor(20/4)=5;
5J=100.
Sum: h = (1 + 36 + 9 + 2 + 5 + 100) = 153 → 153 mod 7 = 6.
Step 4: Map to weekday
Zeller mapping: 6 → Friday. So 1 Jan 2010 = Friday.
Final Answer:
Friday → Option C
Quick Check:
New Year 2010 is known to be Friday ✅

Quick Trick: Remember to decrement the year for Jan/Feb conversions before computing K and J.

Common Mistakes:

MISTAKES

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