What was day of the week on 21-September-1987?

Solution (By Examveda Team)

Formula : (Date + Month code + No.of years + No.of leap year + Century code)/7
$$\eqalign{ & = \frac{{21 + 6 + 87 + 21 + 0}}{7} \cr & = \frac{{135}}{7} \cr & = 2 \cr & = {\text{Monday}} \cr} $$