This site explains how to calculate in your head (in often less than one second) the day of the week for any calendar date. It also explains how to calculate the day, month or year when one of those other elements of a date is unknown but the day of the week is known. There is no faster or simpler formula out there.
The result you got for the above question #7 was actually the value for the Day of the Week the corresponding date fell on. What Day of the Week was that?
