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.
If you answered Thursday or 5 (total 89 minus 84 (highest multiple of 7 in 89) equals 5, which is Thursday), give yourself 10 points. (The date, by the way, is either September or December 25, 1845.)
