Yesterday, I saw footage of some autistic "idiot savants" (I hate that term) - and one fake. There are prodigies, mostly musical prodigies, but there are also people being passed off as something they aren't. The fake was a common one: give him a date and he can tell you what day of the week it fell on. That's a parlor trick. I can do it and you can learn how to do it in an hour or so. Here's how to do it for any date since 1900, using today as an example.
Casting out 28's
There being seven days a week and a leap year every four years, calendars repeat every 28 years. So, take the year and subtract 28 until you get as close to 1900 as you can. Then keep the last two digits.
Example: 2010-28=1982-28=1954-28=1926. Running total: 26.
Add leap years
There's a leap year every 4 years, so divide the number above by 4 and add the whole number.
Example: 26/4=6 (ignoring remainder). Running total: 26+6=32.
"Thirty days hath September..."
This part takes rote memorization. There's a number to add for specific months:
Add 0 for January or October.
Add 1 for May
Add 2 for August
Add 3 for February, March or November
Add 4 for June
Add 5 for September or December
Add 6 for April or July
Example: April=6. Running total: 32+6=38.
Add the date
Example: Today's the 30th. Running total: 38+30=68.
Correction for leap year
Years evenly divisible by 4 are leap years. In those years, you have to add 1 for all months except January or February.
Example: Running total: still 68.
Cast out 7's.
There being seven days per week, it's time to simplify.
Count that many days from Sunday.
Example: Sunday + 5 days = Friday.
So... today must be Friday. But then you already knew that! You must be a genius!!!
6 days ago