This is a cool video of mathemagician, Arthur Benjamin, doing lightning fast calculations in his head. He races a team of calculators to figure out 3-digit squares and tells people from the audience what day of the week they were born on. This is some pretty impressive stuff.
When he was asking for a three digit number I was kinda disappointed no one said 768.
Well that was because everyone knows that its impossible to calculate the square of 768.
? Pretty easy: 589,824. Unless you actually meant square root, in which case, the answer is: 27.712812921102035 
I believe that was sarcasm
Hopefully you weren’t being sarcastic, so that I’M the one that got fooled!
Maybe. A 
usually helps remove any doubt… 
Uh oh! You were editing, and now I’m confused!:o
Of course it was sarcasm. I usually don’t use emoticons because I like it when people don’t know if I am being sarcastic, at least not right away. It’s kind of like when people put effort into deceiving somebody for the purpose of a joke, but then say “just joking!” right away. I don’t like that either because it ruins the point of the joke and any effort that was put into it was in vein.
My first impression was that you were, indeed, using sarcasm, lol. I was just having fun with numbers, haha. 
He not only comes off as really cocky to me everytime he says “thank you very much” But he also comes off as a complete nerd. Maybe not as nerdy as the folks that bring calculators to the talk though.
It probably stems from insecurity and the fear-real or not-that the audience might not applaud soon enough, or at all, after each demonstration. So when he says “thank you very much”, what he really means is: “Ok I finished the trick so please applaud now!”
Bah, It’s just middle school level math. Grade school level if you were educated in Japan.
College if you were educated in the US.
I’m told that I’m at the level in maths everyone else would be at if we were in Japan.
…I’m a junior in high school, and there are some college seniors in my class…and I’m pretty lousy at arithmetic, to be honest. Just this morning I said that 14+7=25.
Haha.
Him saying “thank you very much” pretty much meant that he was finished, and he was obviously just being confident that he would get an applause. I think that confidence is a big part of being a good performer.
Also, I’m pretty sure that this was at some kind of science and technology conference, which is why he could pretty much assume that at least a few people would have calculators.
My middle school math teacher always told us never to assume because you’ll just make an ass out of u and me. Thus assumptions are bad. QED
Then you take a college level course that covers mathematical induction and the first part of the proof is “first assume that the result is true”. Damn. Everything I learned in middle school and high school was wrong.
Talking of maths tricks and stuff:
I read this the other day in Fortean Times
111,111,111 x 111,111,111 =
12345678987654321
Which is a totally useless piece of information but pretty neat.
[QUOTE=Mikefule;1304937]
[B]Talking of maths tricks and stuff:
I read this the other day in Fortean Times
111,111,111 x 111,111,111 =
12345678987654321
Which is a totally useless piece of information but pretty neat.[/[/B]QUOTE]
It is one of a series Mike:
11 x 11 = 121
111 x 111 = 12321
.
.
111111x 111111 -12345654321
.
etc
Anything with a lot of 1’s in it is prone to giving some interesting answers. Some more examples: and you might experiment further yourself.
11 x 111 = 1221
111 x 1111 = 123321
111111 x 1111111 = 123456654321
11x 1111 = 12221
1111 x 111111 = 123444321
Loses some of its neatness once carries get involved of course.
Way back a guy called Trachtenberg wrote a book on making mental arithmetic easy. The multiply by 11 was probably the easiest of the suggestions he made.
I didn’t watch all of this. The first part, squaring 3 digit numbers, is not even arithmetic. If you think about it you only have to memorize about 900 numbers. If you include all of the 2 digit squares it’s about a thousand numbers to memorize and they’re only 6 digit numbers. Realistically, they’re only 5 digit numbers because the key already tells you the last digit. Those keys are 1 to 1, 2 to 4, 3 to 9, 5 to 5, 6 to 6, 7 to 9, 8 to 4, and 9 to 1.
As the guy starts out, he asks the square of something like 5 which everyone knows is 25. I used to know all the squares up to 30 because it was useful to me. Someone can ask me the square of 17 and still I immediately know it’s 289. Numbers like 18 and 19 have faded and there are only a couple of the twenties that I still know. I can see that easily being extended to a thousand keys and answers. You people who predate the cell phone era, how many 7 or 10 digit numbers had you memorized with keys like work, home, mom, Frank, Daisy, Pizza Hut, Dial-a-Prayer etc.?
The second part becomes tricky. It involves the missing digit in a multidigit representation, the sum of which is probably a constant derived from the base number. Again, it’s arithmetic, not math. Deriving the algorithm to apply to each trick is an exercise in mathematics. Applying the algorithm is just arithmetic. For example, determining the algorithm for testing an integer’s divisibility by 3 is a math problem. Applying that algorithm (the sum of the digits is divisible by 3) is arithmetic. The tests for divisibility by numbers like 7 or 11 are somewhat more complex, but not much.
Is this one of those times I am supposed to assume sarcasm?
Mathematical induction involves assuming a starting case to prove subsequent ones. Still you don’t rely on the assumption, in fact that is proven in the basis, which is usually put first in a proof.
Still, using “if” instead is a nice compromise.
And it will be noted that the mathemagician was carrying spare calculators in his pocket. [WINKING EMOTICON]