With a dash of math, know the day of the week for any date on the calendar. The calendar is a mathematical object with regular patterns, such as leap years happening every four years. This results in your birthday increasing by one or two days as you go from one year to the next in a very predictable pattern. Using easy mnemonics, and by adding three numbers together -- derived from the month, date, and year -- the total yields the day of the week. This is a practical application of something ca