February 20, 1999 was Saturday. What day of the week was on December 30, 1997 ?

Ans:

The year during this interval was 1998 and it was not a leap year. Now,

we calculate the no. of odd days in 1999 up to February 19 :

January 1999 gives 3 odd days

19 February 1999 gives 5 odd days

1998, being ordinary year, gives 1 odd day

In 1997, December 30 and 31 give 2 odd days

Total no. of odd days = 3 + 5 + 1 + 2 = 11 days = 4 odd days

Therefore, December 30, 1997 will fall 4 days before Saturday ie on Tuesday.