What was the day of the week on 31 January 2009?

Saturday Sunday Monday Friday

Saturday

Using Code Method :- \(\frac{Date+Month code+Year code+Last 2 digits of yr+Leap yrs till given yr}{7}\) (Note: Remainder of the above sum will be the code of week day}   31 Jan 2009; 31 + 01 + 06 + 09 + 02 = 49 remainder of \(\frac{49}{7}\) = 0 Therefore, the code of 0 is Saturday