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Channel / Source:
TEDx Talks
Published: 2013-04-08
Source: https://www.youtube.com/watch?v=e4PTvXtz4GM
well good afternoon ladies and gentlemen my name is art Benjamin and I am a math magician what that means is I combined my loves of math or I should say maths and magic to do what I call mathematics but before I do before I get started I got a quick question for the audience by any chance did anyone anyone here in the audience happen to bring
with them this afternoon a calculator if you have one perhaps on your phone or saw or somewhere in your pretty comfortable using it raise your hand I'll need a couple of people to help me out here I see one two and perhaps one more of three with the three of you bring out your calculators and join me up here on stage and let's give these volunteers
a nice round of applause from out great over on the side weeks awesome now since I have not had the chance to work with these calculators I need to make sure that they are all working properly would somebody get us started by giving us a two digit number please how about a two digit number just yelling out of some you we okay that's fine seventy four
and another %HESITATION about another two digit number about on the side thirty nine multiply seventy four times thirty nine on the calculator make sure you get two thousand eight hundred eighty six or the calculators are not working to each of you get two eight eight six give them a round of applause now I notice that took some of us a little bit of time to get
the answer that's okay I'll give you a short cut for multiplying even faster on the calculator there's something called the square of the number which most of you know is taking a number and multiplying it by itself for instance five squared would be twenty five six squared would be thirty six seventy three squared would be something else yeah so now I'm most of these calculators a
little shortcut buttons that allow you to square numbers even faster when I'm gonna try and do is to square knew I tested my treatments were five or six with it but I'm gonna try and do is to square in my head three two digit numbers faster than they can do on their calculators even using the short cut method when last is three people how about in
the third row here one two three each yell out a two digit number and if you would square the first one the second and the third one I will try and race you to the answer so quickly a two digit number please twenty four great next toys that ninety eight and one one more twenty six would you call out your answers please five seventy six nine
thousand six hundred four six seventy six give them a round of applause let me try to take this one step further I'm going to try to square some three digit numbers this time I won't even write these down I'll just call them out as they're called out to me anyone at all quiet a three digit number anyone on our panel verify the answer now if I
get the answer right give me a big thumbs up if I make a mistake let me know and I'll try and fix it a three digit number anyone five seventy six is three hundred thirty one thousand seven hundred seventy six yes good how about another round how about another three digit number Sir a three digit number one hundred three is ten thousand six hundred nine way
too easy another three digit number three digit number please one two five is fifteen thousand six hundred twenty five but that's five of the six powers so that was easy to put another up put on a three digit number Sir ninety five is nine hundred seventy thousand two hundred twenty five yes thumbs up if it's right one more out one more three digit numbers are nine
twenty six is a hundred fifty seven thousand four hundred seventy six thank you very much let me try to take this one step further going to try to square a four digit number this time I'm not going to beat you to the answer on this one but I will try to get the answer right to make this a little bit more random have what we use
the fourth row four people each of you quiet a single digit between zero one nine that will be the four digit number that all square one five seven seven one five seven seven this will take me a little bit of time so bear with me three million four hundred eighty six thousand nine hundred twenty nine no okay with both of them coming from with the one
what number was one five seven seven away we train three million so far so good Jose where one high heel I never make a mistake arguing with the two million with everything else right thank you very much what's one million offer clients then I would attempt to square a five digit number and I can but unfortunately most calculators can I so since we've reached the limits
of our calculators although some of yours may go higher I'm going to try to conclude the first part of my show by trying something even trickier let's take the first number on the board here five hundred seventy six which which answer five seven six on your calculator and instead of squaring at this time I'd like you to take that number and multiply it by any four
digit number that you want but don't make it too easy like one thousand or one two three four but just some random four digit number so you should have as an answer either a six digit or possibly a seven digit number how many digits are in your answer six or seven digits seven seven six is there any possible way that I could know what six or
seven digit numbers they have say now good then I shall attempt the impossible or at least the improbable what I'd like each of you to do is to call out for me any six of your seven digits or in your case five of your six digits in any order you like one digit at a time I shall try and determine the digit you've left out so
starting with your six digit number call out any five of them please eight zero nine three eight did you leave out the number eight yes that's one you've got a seven digit number called any six of yours loud and clear did you leave out the number six that's true the odds of me getting all three of these right by pure guessing would be one in one
thousand ten to the third power okay any six of your digits really scrambled up this time did you also leave out the number six great let's give all three of these people but I throw a little pause thank you very much well for my next number I have another question for the audience by any chance does anyone here happen to know the day of the week
that they were born on if you think you know your actual birth day raise your hand up I starting with you what year if I may nineteen ninety two and what month July what third was that a Friday yes excellent somebody else I yes Sir green sure what you're nineteen ninety two in the month June what thirtieth was that a Tuesday excellent somebody else la how
about you what year I'm sorry so what year was it nineteen ninety five and what month June what twenty six was that a Monday excellent when I see a hand up in the balcony ya a young lady I'll try something different here you're sure the birthday what I'm on what what year was it what what what what what day of the week was a tell me
an advance the day of the week Thursday okay and what year was it two thousand two what did happen to be on may second yes but that's my daughter I knew that one I was there for that one that Thursday anyway I hundreds tried that before Belinda I do we have anybody here who does not know the day of the week they were born but would
like to find out I'm okay now let's see I I see yourself course if you don't know what it is I could just make up an answer and you probably believe me but I don't want you to have to do that so I come prepared for that situation there is an app for everything these days so %HESITATION I asked one of you here just to take
this and are so give us your year and then type in the year right on that point but what you're nineteen ninety five so type in nineteen ninety five great and what month September press the September button there and that should give you a calendar us September what twenty first I believe was a Thursday can we get confirmation it was Thursday could I tell you what
I you know it since you have the app with you let's try something trickier %HESITATION then the app actually goes as far into the future as three thousand as far back into the past as sixteen hundred don't go below sixteen hundred because then we get off the Gregorian calendar in that messes me up a little so what what year would you like choose a year between
sixteen hundred and three thousand go ahead two thousand seven hundred thirty so enter two thousand seven hundred thirty into that and what month would you like June what thirteenth will that be a Friday yes and it'll be cloudy on that they too if I'm not mistaken thank you very much in fact anybody else who wants to find out their birth they see me out at in
the lobby perhaps in the breaker so I'll be more than happy to tell you now I just a little bit of time left side like to do one last thing for you that I alluded to earlier when we had the other calculators on stage I'm going to try to square a five digit number requiring if you have a ten digit calculator or higher fuel bills would
feel free to bring out your calculator at this point on and but to make my job more interesting for you as well as for me I'm going to do this last problem thinking out loud so you can actually honestly hear what's going on in my mind while I do a calculation of this size let's create a five digit number how about we go I'll just go
up of this I own the first five people along the aisle each give me a single digit that will be my five digit number three seven six nine one thirty seven thousand six hundred ninety one the squared yuck let me explain to you how I'm going to attempt this problem gonna break the problem down into three parts how do thirty seven thousand squared plus six hundred
ninety one the squared plus thirty seven thousand times six ninety one times to and all those numbers together and with anti lock arrive at the answer now let me explain one more thing while I do this calculation you might hear certain words as opposed to numbers creep into the calculation let me explain what that is this is a fanatic code a mnemonic device that I use
that allows me to convert numbers into words I store them as words and later on we treat them as numbers I know it sounds complicated it's not I just don't want you to think you're seeing something out of rain man here there's definitely a method to my madness definitely definitely you can start one last instruction for my judges with calculators now who's got an answer in
front of them raise your hand okay enough of you there is a fifty percent chance that I will make a mistake on this problem if I do don't tell me what the mistake is just say you're close or something and I'll trying figured out which can be pretty entertaining in itself if however I am right whatever you do don't keep it to yourselves make sure everybody
knows that I got the answer right because this is my big finish okay so without any more stalling here we go ostocka problem the middle with thirty seven times six ninety one now that's the only guy says that seven hundred minus nine of the commands that a seven hundred times thirty seven twenty five thousand nine hundred thirty seven times honestly thirty three subtract the two to
get twenty five thousand five sixty seven twenty five thousand %HESITATION do I believe that you twenty five thousand five sixty seven double that to get fifty one thousand one hundred thirty four fifty one thousand one hundred thirty four okay fifty one thousand becomes like tomorrow like tomorrow is fifty one thousand one hundred thirty four that seems right I'll go on next thirty thirty seven squared which
is one three six nine so I can say one billion take the three sixty nine have that to like is there gonna be carrying a three sixty nine and that's like get four hundred twenty million tomorrow tomorrow okay next we do six ninety one square that seven hundred times six eighty two plus nine squared it forms of the seven thousand four eighty one raft if I
