The 19th of September 1987 was a Saturday. If 1988 was a leap-year, what day of the week was the 21st of September 1990?	Choose the correct choice
A) Monday B) Tuesday C) Wednesday D) Thursday E) Friday
There are 365 days in an ordinary year and 366 days in a leap-year.   365 divided by 7 (a week period) yields a remainder of 1, thus the same date after an ordinary year would fall on the next day of a week;   366 divided by 7 (a week period) yields a remainder of 2, thus the same date after a leap-year would fall two days after in a week;   Thus 3 years, 1988, 1989 and 1990, will accumulate   2+1+1= 
<gadget id="calculator">  2+1+1</gadget>
<output>4</output>
4 days, plus 2 days of difference between 19th and 21st, which gives total of 6 days of difference (6 days shift). Thus, 21st of September 1990 was Saturday+6 days=Friday.   Answer: Friday.
<result>E</result>
The 19th of September 1987 was a Saturday. If 1988 was a leap-year, what day of the week was the 21st of September 1990?