Does anyone know how to do this old "mentalist" trick?

I had a friend in college who, if given any date in history, could tell you what day of the week that date fell on. I used the perpetual calendar from my trusty World Almanac to check him and he was always right. Example, I’d say, “August 12, 1821.” He’d pause a second or two and say, “Sunday.” Said it was a pretty simple formula, and he taught it to me but I’ve long since forgotten.

This was a trick that the real “Rain Man” could do also, as he proved in an interview with Morley Safer on “60 Minutes” some years ago. (Morley held the World Almanac on him too.)

Can anybody teach me how to do this truly MP trick?

I put “Day of the week formula” into google and thiswas the first site.

Thanks, DG!

Wow! I meant to add that my friend was pretty smart – he wasn’t a savant. I’m not sure I could learn this formula at my age and what does it matter? It’s just a silly party trick but it can be impressive.

If you like that kind of tridk, here’s something cool. This website “knows” which number you have chosen from its list. It really does! Check it out!

The Flash Mind Reader can tell what you’re thinking! It’s eerie! It’s wonderful! It’s fantasmagorical!

Ok I checked DD site, how does it do it?

That site… if you look carefully, the numbers change each time it is refreshed. Choose any number, do the formula in your head, and you’ll see that it’s all the same result - which is the one displayed when you click on it. It’s a fun site, but easy to figure out. =)

Choose any number. The answer has to be a multiple of 9:

(10x + y) - (x + y) = 9x

Look at the chart, every multiple of 9 has the same symbol.


Yeah, that’s a pretty cute trick. That formula always returns a multiple of 9. All the symbols for the multiples of 9 are the same. (Except for 90 and 99, just to make it harder to spot—but you can’t get those numbers using that formula.) Then they change at each refresh.