Problem
You might want to know what day of the week your birthday is this year. Mathematician John Conway invented an algorithm called the ‘Doomsday Rule’ to determine which day of the week a particular date falls on. It works by finding the ‘anchor day’ for the year that you’re working in. For , the anchor day is Friday. Certain days in the calendar always fall on the anchor day. Some memorable ones are the following:
‘’ of March - which is th February in a leap year, and th February otherwise.
th April, th June, th August, th October and th December. These are easier to remember as , , , and .
th May, th July, th September and th November. These are easier to see as , , and . A mnemonic for them is “9-5 at the 7-11".
Then find the nearest one of these dates to the date that you’re looking for and find remainders.
For example, day, (th March, which is written in American date notation. It’s also Albert Einstein’s birthday) is exactly days after ‘’th March, so is the same day of the week - Friday in .
What day of the week will th December be in ?