If 28 February 2020 was Friday, then what was the day of the week on 30 December 2015?

Wednesday

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 }

28 Feb 2020;

28 + 03 + 6 + 20 + 05 = 62

remainder of \(\frac{62}{7}\) = 06

Therefore, the code of 06 is Friday 

Similarly,

30 Dec 2015

30 + 06 + 06 + 15 + 03 = 60

remainder of \(\frac{60}{7}\) = 04

Therefore, the code of 04 is Wednsday