How do you work out on which day of the week a particular date falls? Assuming you don't have a calendar handy, that is?
Method 1: This handy algorithm (click).
Too complicated? Thought so.
Method 2: Learn this 12-digit number off by heart - 155274263153
For 2005, this number tells you the date of the first Saturday in each month. So, January 1st 2005 is a Saturday, and so are February 5th, March 5th, April 2nd, etc. To work out other days in each month just count on from the one day you know. (For example, want to know the date of Christmas 2005? Well, December 3rd is a Saturday, and so must be December 10th, 17th and 24th, and so Christmas Day must be a Sunday). For 2006 use the same number to give the date of the first Sunday in the month, for 2007 the first Monday, and so on. Bit of a problem with leap years though - for 2004 the number gives you Thursdays in January and February, but Fridays from March onwards.
Method 3: Use the Doomsday algorithm
Nothing to do with the end of the world, but a supposedly-simple way to calculate days of the week invented by the famous Liverpool mathematician JohnConway. It's rather like the previous method but without a 12-digit number to memorise. Each year has its own so-called Doomsday, and Doomsday is always the last day of February. For 2004, February 29th is a Sunday, so Doomsday is a Sunday. In the other even-numbered months, 4/4, 6/6, 8/8, 10/10 and 12/12 are all Doomsdays (Sundays). Odd-numbered months are trickier to remember, but 9/5, 11/7, 5/9 and 7/11 are all Doomsdays (works in the US as well as the UK, thankfully). As for March, that begins on the day after Doomsday, and then there's January... But if you've followed this so far, I suspect you'd be better off reading the proper instructions - here. Bit tricky, especially working dates out in different years, but it is dead clever.
Method 4: Cheat
Even if you don't understand the Doomsday algorithm, this bloke does. Just type the date into his webpage and his program will work out the day of the week for you.
Method 5: Cheat properly
Choose any year from 1582 to 3000 and find the whole calendar here, or here.
Week daze
