Lightning calculation and other "mathemagic" | Arthur Benjamin

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  • čas přidán 8. 01. 2008
  • www.ted.com In a lively show, mathemagician Arthur Benjamin races a team of calculators to figure out 3-digit squares, solves another massive mental equation and guesses a few birthdays. How does he do it? He'll tell you.
    TEDTalks is a daily video podcast of the best talks and performances from the TED Conference, where the world's leading thinkers and doers are invited to give the talk of their lives in 18 minutes -- including speakers such as Jill Bolte Taylor, Sir Ken Robinson, Hans Rosling, Al Gore and Arthur Benjamin. TED stands for Technology, Entertainment, and Design, and TEDTalks cover these topics as well as science, business, politics and the arts. Watch the Top 10 TEDTalks on TED.com, at
    www.ted.com/index.php/talks/top10
  • Věda a technologie

Komentáře • 981

  • @NateBagley
    @NateBagley Před 10 lety +328

    I've never rooted so hard for someone to do a math problem.

    • @TeamRetox
      @TeamRetox Před 9 lety +1

      That cracked me up

    • @escargoux
      @escargoux Před 8 lety

      *****
      I was thinking the same thing. It was very suspenseful, like close soccer game.
      I would watch mathematician competitions on TV, lol

    • @daniel01231
      @daniel01231 Před 5 lety +1

      @@escargoux whoosh

    • @oscara.3981
      @oscara.3981 Před 4 lety +4

      Hahahaha rooted

  • @kwilson5832
    @kwilson5832 Před 11 měsíci +27

    "I know as a magician, we're not supposed to reveal our secrets, but I'm not too afraid that people are going to start doing my show next week" Classic!

    • @GMYC7774
      @GMYC7774 Před 5 měsíci +2

      Yeah, not even 15 years later. Legendary!

  • @Durzo1259
    @Durzo1259 Před 8 lety +596

    This guy's pre-frontal cortex must be a quad-core.

  • @arthurwoster4856
    @arthurwoster4856 Před 4 lety +83

    teacher: no calculators allowed in tests
    me: brings arthur benjamin
    teacher:

  • @chesseswar
    @chesseswar Před 8 lety +338

    Oh, the days before everyone had a calculator on their phones.

  • @xw591
    @xw591 Před 2 lety +19

    More than just impressive, he seems like a genuinely great guy, great humor.

  • @rrahman12
    @rrahman12 Před 3 lety +35

    A fantastic guy. Really deserves a standing ovation.

  • @HemoStopRomania
    @HemoStopRomania Před 8 lety +33

    I just love this guy. He's incredible.

  • @Renato404
    @Renato404 Před 15 lety +35

    loved it when he showed no problems in revealing his methods. Amazing!! Dam good!!!

  • @Jalanko13
    @Jalanko13 Před 13 lety +16

    This guy is great! it's one thing to be a math genius...it's another to know how to work a crowd.Seriously, the way he keeps the audience enthralled and inserts light humour "Let me re-cap *puts cap back on*" is a great way to ease the audience.Wow. Great Going Art :)

  • @isabellajimenez7072
    @isabellajimenez7072 Před 10 lety +31

    My sister has his "the Great Courses: The Secrets of Mental Math" She is absolutely amazing! She can finally square 5-digit numbers in her head, though it takes roughly 2-3 minutes.

    • @SpiritMolecule
      @SpiritMolecule Před 9 lety

      *****
      sarcasm?lool

    • @isabellajimenez7072
      @isabellajimenez7072 Před 8 lety

      Wow you're so classy... She goes to math competitions and wins, thank you. That's how she applies this knowledge.

    • @isabellajimenez7072
      @isabellajimenez7072 Před 8 lety

      Well that's obvious, but for now, it's quite useful...

    • @94D33M
      @94D33M Před rokem

      @@isabellajimenez7072 are you still there mate

  • @DisKeda
    @DisKeda Před 9 lety +97

    What I liked about this that the guy was actually funny.
    You wouldn't expect it from this kind of person.
    Very good!

  • @HelloDapp
    @HelloDapp Před 5 lety +15

    this guy has to have that talent where he can remember every detail of his life

  • @vika09
    @vika09 Před 14 lety +8

    It's a mind blowing application of the (a+b)^2 and (a-b)^2 formulas.
    Still a damn genius.

  • @theplayersplay1984
    @theplayersplay1984 Před 8 lety +121

    1:27 He almost said the word stupid

  • @groundshaker333
    @groundshaker333 Před 11 lety +12

    Saw this live today, he came to our school and he truly is amazing!!! Amazing work !!!!

  • @anshulgoel007
    @anshulgoel007 Před 10 lety +60

    Nice viewing.. But two mistakes
    457^2 = 208849 [Not 208549],
    722^2 = 521284 [Not 513284]
    I guess the people with the calculators on stage doubted themselves / were embarassed to point it out.
    But still amazing to do this in so short a time.

    • @blahblaah4474
      @blahblaah4474 Před 10 lety +5

      For 457 squared I heard him say 205849 but my calculator gives me 208849.

    • @Ishaanstube
      @Ishaanstube Před 6 lety +7

      Were the people with the calculators retards or something, couldn't read out the correct answer or were too shy to correct him.

    • @foya7404
      @foya7404 Před 4 lety +5

      Anyhow, his performance is still absolutely remarkable as he only did two mistakes in over 50 calculations

  • @mariah98nelson
    @mariah98nelson Před 11 lety +11

    I got the book.
    He's phenomenal!

  • @NectarineSoup
    @NectarineSoup Před 10 lety +356

    This man is banned from all casino's in the state of Nevada.

    • @CodingMazaa
      @CodingMazaa Před 6 lety +3

      why?

    • @nickbirrer
      @nickbirrer Před 6 lety +18

      kumropotashify He would destroy the house every goddamn time.

    • @preciousdoe6813
      @preciousdoe6813 Před 3 lety +2

      Why?

    • @wooty2745
      @wooty2745 Před 3 lety +8

      @@preciousdoe6813 he can count for example: cards and odds. but ofcourse hes not banned.

    • @whiterajah2072
      @whiterajah2072 Před 2 lety +3

      Not if he's performing there 🤪

  • @CaseysBeats
    @CaseysBeats Před 8 lety +74

    Oops, I see a carry coming.

  • @mateharris
    @mateharris Před 16 lety +4

    Art, you rock! Art Benjamin is a professor where I went to college, Harvey Mudd College. Despite knowing him for years, I am still in awe at his mental math ability.

  • @PolochAngriff
    @PolochAngriff Před 7 lety +176

    When he asked the audience what 5 squared was, I blurted out the wrong answer..

    • @BlessedOne686
      @BlessedOne686 Před 5 lety +1

      😂😂😂

    • @davidweng2160
      @davidweng2160 Před 4 lety

      Ok boomer

    • @cher4057
      @cher4057 Před 4 lety +5

      David Weng you’re using it wrong...

    • @davidweng2160
      @davidweng2160 Před 4 lety

      Chen H would you be so nice as to teach me then?????

    • @triple7marc
      @triple7marc Před 4 lety +3

      David Weng It’s not funny regardless of how you use it. But it’s especially not funny when it makes literally no sense, like how you just used it.

  • @alisonhernandez7189
    @alisonhernandez7189 Před 6 lety +2

    My class invites you to our school. I have showed this video so many times to so many classes. Every year my students are amazed. Some of them say you are their idol because of your mental math skills.

  • @claudees
    @claudees Před 14 lety +4

    Truly appreciate Arthur Benjamin's efficiency, intelligence and eloquence. Thanks for sharing this video. Best wishes.

  • @audimute
    @audimute Před 16 lety +3

    I was impressed... yes with "the show/ presentation" but more so, how fast my 2kids picked up mental math as a game. You gotta get this guys book! It makes math very "useful" for everyone. I wonder why schools have not picked up some of his methodology. It is so musch easier than how traditional math is tought. When you look past the showmanship of this video, there is real science, genious, and surprisingly FUN. Very impressive Mr. Benjamin. Best of luck to you.

  • @StayQrious
    @StayQrious Před 9 lety +64

    Interestingly, in the trick, 8649 is a multiple of 9 which means that any multiple of it will also be a multiple of 9. The test for divisibility for nine is that all the digits added will still give a multiple of 9 if done recursively and so we can just add the remainders with 9. (ie. 81(8+1) , 8649 ( 8+6+4+9 = 27, 2+7 = 9) . We don't have to even go this far in addition. We can keep subtracting 9 as the sum becomes greater than 9 and that's all he does with his showmanship of course, eg.
    He took 8649 because it was convenient,
    (he says six digits in "any order" because the order of the sum of the digits hardly matters. A middle school student knows this.
    person 1 -1,9,7,0,4,0 - (find the sum subtracting 9 every time the sum exceeds 9 and you get 3 - so the number to be added to this to reach 9 would be 6 and that's what he says.
    person 2 - 4,4,8,7,5,2 - circular sum = 3 therefore answer = 6
    Person 3 - 0,7,9,0,4,4 - circular sum = 6 . Ans = 3
    Person 4 - 2,6,3,9,7,2 - circular sum = 2. Ans = 7.
    Loved the way he pulled off a middle school question with all that showmanship.

    • @Bobstew68
      @Bobstew68 Před 9 lety +4

      Nice work figuring this out! I was hoping the comments would contain something like this.

    • @youvegottobefukin
      @youvegottobefukin Před 9 lety +1

      aanand srinivas Yeah I go that too. Nice trick though

    • @Keyakina
      @Keyakina Před 9 lety +3

      aanand srinivas didn't even get this

    • @mattt3942
      @mattt3942 Před 6 lety +1

      It is not a random coincidence that 8649 is a multiple of 9, either. The way he got these numbers was by calling 4 people in a row, with the last being on the end. He did the exact same procedure in another video I've seen him do this trick. Again, the last choice was a girl on the end of the row who served him up a number divisible by 9. This is a trick which I think is beneath this man. All of the other calculations he does are completely legitimate and can be learned from. This trick only works when his "plant" in the audience serves him up a number divisible by 9.

    • @omak7084
      @omak7084 Před 6 lety +5

      an easier way dude, is to just add all the numbers, and subtract it from the next multiple of 9. example: 1 + 9 + 7 + 4 + 0 + 0 = 21. 27 - 21 (next multiple of 9) = 6.

  • @brandon7477
    @brandon7477 Před 10 lety +16

    I don't know if this is how he did the missing digits trick or if it was just a coincidence: the number he chose, 8649 is divisible by 9 and I know this because if you add all the digits, you get 27 which is 9*3. The is the divisibility rule for any multiple of 9. If you multiply 8649 by a 3 digit number, it will still be a multiple of 9 and thus the rule still applies. For example, if they told you that 6 digits were all 1's, then you would know that the last digit is a 3.

    • @theraymondchou
      @theraymondchou Před 10 lety +1

      That's exactly what he did. Notice how he picks the one number that is divisible by 9. The day of the week thing he uses an algorithm for, though he said 1824 is hard implying he's using "anchor dates," which is really inefficient imo, there are better ways.
      The three digit squares he talks about in his book, and he's so well versed in it it becomes almost lightning like.

    • @jimmierustler5607
      @jimmierustler5607 Před 10 lety +1

      Ray Chou
      Might have been because 1824 was a leap year

    • @mikelincoln8395
      @mikelincoln8395 Před 5 lety +1

      This is just like knowing all the necessary moves to manipulate a Rubric cube, then practise practise practise.

  • @mantingfoo8697
    @mantingfoo8697 Před 7 lety +76

    He must have eaten a calculator when he is 1 year's old

  • @Repented
    @Repented Před 15 lety +9

    Wow, amazing! He's well articulated, talented, and entertaining as hell.

  • @opalseekingthetruth7620
    @opalseekingthetruth7620 Před 7 lety +5

    This was amazing to watch. - Definitely not the same as this video, but sometimes I give my son math problems just on a whim to solve, and I gave him 97+49 ...He gave me the answer from his head before I could. :P He's 7. lol You would think I'd be embarrassed to tell that story, but nope. Too proud of him to care. :P If he's a natural mathematician, I will definitely support and encourage his development in that subject.

  • @johnnytheyoungmaestro

    Wow, a standing ovation! Arthur Benjamin is really talented, and he's so great at adding humor to all of this! :)

  • @alexrobertsfcim
    @alexrobertsfcim Před rokem

    The first time I remember seeing this video was in my pre-calc class junior year of high school back in 2010-'11. The video is so good that I keep coming back to it now several years since I finished school.

  • @pablopablopablo22
    @pablopablopablo22 Před 13 lety +19

    "someone give me a 3-digit number."
    "100."

  • @pop12Viper
    @pop12Viper Před 9 lety +40

    First I said: wow he is a math genius. Then I said: wow he is a time traveler.

  • @RadheadFilms
    @RadheadFilms Před 12 lety +2

    This guy is my math teacher at Mudd. He's awesome.

  • @riccardoportelli4065
    @riccardoportelli4065 Před 5 lety +1

    This show's script if identical to his Ted talk 5 years later it's almost insane. I can't believe he did the exact same show over and over for that long.

  • @highflyer7652
    @highflyer7652 Před 14 lety +4

    This is so awesome, I am really at awe. I''ve bought his book before I saw this video, now I'm gonna read it

  • @michaelmcclung4193
    @michaelmcclung4193 Před 8 lety +37

    Lol, same exact thing in another TEDx Talk

  • @deepak201
    @deepak201 Před 11 lety +1

    Thousands still do it in India. Shakuntala Devi is a famous and much venerated Indian mathematician who is considered a genius and is popularly known as the Human Computer. In 1977, Shakuntala extracted the 23rd root of a 201-digit number mentally, 12 seconds faster than the Univac-1108. She even occupies a place on the 1995 Guinness Book of Records for her skills.

  • @ajayprasanna9217
    @ajayprasanna9217 Před 3 lety

    that standing ovation atlast gave me goosebumps

  • @marcellocapone4925
    @marcellocapone4925 Před 9 lety +70

    I get a hint this gentleman is good at maths. Just a hint though...

  • @anncervales1492
    @anncervales1492 Před 9 lety +19

    I actually watched this clip more than twice.

    • @Mike-dy8sj
      @Mike-dy8sj Před 6 lety

      Ann Cervales more than twice? You can't count higher than that?

  • @spacedtime6597
    @spacedtime6597 Před 15 lety

    Sounds right, These guys put so much work into a small tricks like this.

  • @jasmineswen
    @jasmineswen Před 13 lety +1

    AMZING!! just unbelievable! My math teacher also impressed!

  • @DjGreydanus
    @DjGreydanus Před 10 lety +3

    8:00 For day of the week trick

  • @an.gie.gie0811
    @an.gie.gie0811 Před 7 lety +8

    I need him as my next math teacher...

  • @quleughy
    @quleughy Před 14 lety +2

    Agreed. Makes me wish I enjoyed algebra more in school.

  • @leonlian007
    @leonlian007 Před 14 lety +1

    He is great in mental math, there is no question about that. I had that experience when I was in grade 5 in China. wht i remember was doing addition and subtraction instead of multiplication, nothing very tricky, coz u still have to memorize all the procedures and number in it.

  • @m12mikeful1
    @m12mikeful1 Před 12 lety +6

    "let me re-cap"....... ahhaah lol nice one. XD

  • @cmanw
    @cmanw Před 16 lety +2

    That was awesome! Wish I could just do the 2 digits in my head!! :)

  • @lilyvingdead
    @lilyvingdead Před 7 lety +1

    Watched this in Math Club and my seat mate who was a fast calculator was mind-blown.

  • @NebraskaBear
    @NebraskaBear Před 12 lety

    I just saw his show in Kearney. It was the best show I've ever seen!

  • @Laxmikanthb1
    @Laxmikanthb1 Před 3 lety +4

    Me returns from grocery store
    Mom: where is the remaining money?
    Me: 13:56

  • @anncervales1492
    @anncervales1492 Před 9 lety +11

    I like him, he's so smart and funny as well!

    •  Před 8 lety +1

      +Ann Cervales are you attracted to him sexually or just like we men are amazed how he is good

    • @anncervales1492
      @anncervales1492 Před 8 lety

      Of course not sexually! Lol

    • @nathan791
      @nathan791 Před 8 lety +1

      +pako pako That's a nice thing to say to someone.. :/

  • @GuardsmanBass
    @GuardsmanBass Před 11 lety

    I'd love to see this live.

  • @Osminiscool
    @Osminiscool Před 14 lety +2

    I just saw this guy on the Colbert Report lol
    He's pretty damn cool!

  • @redmed10
    @redmed10 Před 7 lety +4

    everybody in the audience are in on it.

  • @dany3241291
    @dany3241291 Před 8 lety +37

    hax, VAC banned.

  • @sk8rdman
    @sk8rdman Před 12 lety +2

    Although I typically frown strongly upon the typical math magic I've seen, I can't help but appreciate the work that this man does and the show that he puts on. Numbers are simple, and with practice, observation, and motivation, It's not surprising that this can be done. There are many unobserved patterns and unpopularized formulas that can make these calculations relatively simple. I am not surprised, and barely impressed, but I am very appreciative of the interest and practice behind it all.

  • @Daniel-pd2zn
    @Daniel-pd2zn Před 8 měsíci

    This guy is so good. Definitely, definitely.

  • @ShephineShaji
    @ShephineShaji Před 10 lety +6

    at 3:42 he made a mistake... 457^2 is 208849 and not 205849 as he said!

    • @AddzyKishoore
      @AddzyKishoore Před 9 lety

      Yeah!

    • @phanduong6170
      @phanduong6170 Před 9 lety +1

      Yeah! The 4 guys in the platform had some gestures like disagreeing with him, but he didn't mind. But this it's just a little mistake. ^^

    • @Grejegando
      @Grejegando Před 9 lety

      Also 722

  • @frankhomer9323
    @frankhomer9323 Před 9 lety +12

    This guy shows some amazing abilities, but can he take out the trash ?

  • @DoLLfaceEMME
    @DoLLfaceEMME Před 8 lety

    Wow This was the most incredible thing I've ever seen!!!! What a gift!!!!

    • @IFrancyISantosI
      @IFrancyISantosI Před 8 lety +17

      why a gift? he had the passion and trained it. we are just too lazy

  • @Bughugger
    @Bughugger Před 3 lety +2

    How am I JUST seeing this!?! He's not only Brilliant, he's HILARIOUS! Thank you Arthur Benjamin!

  • @konstantingeist3587
    @konstantingeist3587 Před 8 lety +4

    A few weeks ago I attempted to multiply a 4-digit number by a 2-digit number... in my dream. I actually remembered my way of calculating it when I woke up and it was correct, but it wasn't finished, unfortunately

    • @opalseekingthetruth7620
      @opalseekingthetruth7620 Před 7 lety +1

      +KonstantinGeist I think dreams could be used as powerful tools if we practice it. ("Practice dreaming?" - I don't know if you're familiar with lucid dreams, but it's where in a dream you KNOW you're dreaming. Therefore could do practically anything you want.) In one of mine, I could speak and understand fluent French. Like it was the most natural thing to do. It'd be amazing if we could tap into this ability. : )

    • @WinstonKnows
      @WinstonKnows Před 5 lety

      Opal SeekingtheTruth I love that concept! I would recall things that I had forgotten(while awake), in my dreams. There has to be a way to tap into our subconscious and draw out ideas, thoughts, memories, data, etc...

  • @laxmanselvam
    @laxmanselvam Před 10 lety +7

    This is insane. I was actually going to bed. then I thought, lets watch a TED talk. I am fresh now.
    *Standing Ovation*

  • @it3basket3ball
    @it3basket3ball Před 7 lety +1

    He did pretty much the exact same thing in a Ted (might have been TedX) talk many years later. Same words and everything, just different numbers haha

  • @Raykon9
    @Raykon9 Před 11 lety +1

    i cant even do a double digit and this guy is......no words, simply amazing

  • @WordsandNumbers1
    @WordsandNumbers1 Před 5 lety +4

    One mistake sir, 1824, June , 6th was actually sunny ⛅.
    Lol

  • @KumareshRamesh
    @KumareshRamesh Před 9 lety +6

    What if someone had left out 0 or 9?

  • @MagicianBrendanRodrigues

    i was priviliged to see arty live a few times, he is very entertaining,

  • @sharmanedeleon831
    @sharmanedeleon831 Před 10 lety +1

    I salute this man,,,he's so smart!

  • @user-cw2py6wh8l
    @user-cw2py6wh8l Před 4 lety +3

    why no one ever pick zero?

  • @poketosonic88834
    @poketosonic88834 Před 11 lety +3

    He just visited our school! :D
    AMAZINGGG

  • @MoonLiteNite
    @MoonLiteNite Před 11 lety +2

    Na, you can easily calculate all the stuff he was doing.
    The day of the week trick is very easy to learn, took me like 4 hours of practice when i was 7 years old.
    SUPER awesome bar trick :)

  • @dparekhEE
    @dparekhEE Před 11 lety

    boy oh boy would that stage be full if this talk was today with calcs on your phone

  • @bishololo
    @bishololo Před 10 lety +5

    Mother of MATH !!!!!!!!!!!!!!

  • @sachinjagarwar
    @sachinjagarwar Před 4 lety +3

    what happened to cookie though .did anyone eat it🤭🤭🤭

  • @AlCampo76
    @AlCampo76 Před 16 lety

    Biologicalscum - when he says "cookie fishin" he is referring to 77862. When he says "revup" he's referring to 489. I don't understand when he says "there is a cary coming". The mnemonic system he used is explained in a book by Tony Buzan - Master Your Memory. You'll have to buy another book for mental arithematics...

  • @naybobdenod
    @naybobdenod Před 13 lety

    very entertaining especially the re-cap lol

  • @poketosonic88834
    @poketosonic88834 Před 11 lety +3

    His intro: Exact same wording he used at our assembly today. :O

  • @aboveaverageinsanity8128
    @aboveaverageinsanity8128 Před 4 lety +6

    "It will take me a little bit of time" it would take me a year.

    • @robinsonpeter7942
      @robinsonpeter7942 Před 4 lety

      Hvis du har brug for hjælp bare besked mig om WhatsApp på +63953150922

  • @101toheedahmad
    @101toheedahmad Před 13 lety

    fantatic mindblowing,he has extrawordinery skills , and commond on the mathematics
    amazing

  • @MissMuffinToYou
    @MissMuffinToYou Před 9 lety +1

    this is beyond cool! i so respect this guy, he has an amazing talent that he must have worked at for a long time. kudos to him

  • @rubic64
    @rubic64 Před 9 lety +14

    722^2=521284 and not as he claimed 113284 4:01

    • @WalterKingstone
      @WalterKingstone Před 9 lety +1

      rubic64 You mean "as he claimed 513284" but you're right! He got it wrong!!??

    • @Grejegando
      @Grejegando Před 9 lety +1

      And the first 3-digit number he also got it wrong

    • @WalterKingstone
      @WalterKingstone Před 9 lety

      987 squared does equal 974169

    • @Grejegando
      @Grejegando Před 9 lety +8

      Sorry, I meant the second one.
      457^2 = 208,849
      He said 205,849

    • @corvoattano8426
      @corvoattano8426 Před 8 lety +1

      +Grejegando he said it wrong. The rest were the same.

  • @jordanrogerson4499
    @jordanrogerson4499 Před 10 lety +25

    No magics just mathematics.

    • @sagitswag1785
      @sagitswag1785 Před 7 lety +3

      Jordan Rogerson well, most of these routines are described in mentalism books...

  • @polarbits
    @polarbits Před 11 lety

    This guy was at my Mathcounts event a year ago!

  • @boobooberry
    @boobooberry Před 16 lety

    lol, "cookie fiscient...i see a carey coming..."XD, we watched that in our English class. The whole classed was totaly stunned.

  • @nts0011
    @nts0011 Před 8 lety +6

    damm killer cpu

  • @brennahill5449
    @brennahill5449 Před 8 lety +6

    my math teacher was in a conference with Arthur Benjamin and beat him at the 24 game

  • @Tino81295
    @Tino81295 Před 11 lety

    doing revision for my maths exam next week...this is the best procrastination so far...

  • @musicvideojunky
    @musicvideojunky Před 15 lety

    Very impressive, agreed. A friend of mine knows the date trick, but it takes him about a minute to tell you what day it is, whereas this guy will tell you in a few seconds. :)

  • @thepussygrabbingfamilyvalu557

    3:41 he's asked about 457*457 and he says 205,849... btut it's actually 208,849

    • @MarkCliffeIsGay
      @MarkCliffeIsGay Před 7 lety +1

      I love your username.

    • @HelloDapp
      @HelloDapp Před 5 lety +23

      back in the day it use to be 205,849 , then they updated maths

    • @rayawira
      @rayawira Před 5 lety

      Nobody's perfect

  • @shahaddaood9468
    @shahaddaood9468 Před 10 lety +4

    he is a human calculator
    nothing beats him

  • @orbital1337
    @orbital1337 Před 14 lety

    I know how he did the second trick: 8649 is divisible by 9. So any number multiplyed with it is going to be divisible by 9, too. As well now a number is divisible by 9 if all digets add up to a number that is divisible by nine. So if you know all digits except 1 you can simply look for the next number divisible by 9 and subtract all the digits from it.

  • @slaballinmytrunk
    @slaballinmytrunk Před 13 lety

    I got his book last summer, but this is the first time I watch him perform. Fucking incredible.

  • @itsjustameme
    @itsjustameme Před 12 lety +9

    I am pretty decent at squaring 1 digit numbers in my head myself :)

  • @megakeenbeen
    @megakeenbeen Před 10 lety +7

    the answer for 722 squared was actually wrong.

  • @aoo1977
    @aoo1977 Před 16 lety

    Thanks!
    Would you please explain more? like to give an example of a 4-digit times a 3-digit, then work it out.

  • @user_0854x0
    @user_0854x0 Před 5 lety +1

    A matemática e a sensação de prazer logo após resolver um grande problema matemático, me fizeram recuperar a auto-estima e sair da depressão.