1st January 2000 AD = 1600 + 300 + 99 + 1 day
Number of odd days in 1600 years = 0
Number of odd days in 300 years = 1
Number of odd days in 75 ordinary years = 75
Number of odd days in 24 leap years = 48
Number of odd days in January, 2000 = 1
Total number of odd days = 125 days = 17 weeks and 6 days
Hence, 1 January 2000 AD was Saturday.