If 12 January 2019 was on Monday, what was the day on 14 December 1917?

Sunday

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 }

12 Jan 2019;

12 + 01 + 06 + 19 + 04 = 42

remainder of \(\frac{42}{7}\) = 0

Therefore, the code of 0  is Saturday + 02 = ( Monday)

Similarly,

14 Dec 1917;

14 + 06 + 0 + 17 + 04 = 41

remainder of \(\frac{41}{7}\) = 06

Therefore, the code of 06 is Friday + 02 = ( Sunday )