Faster than a calculator | Arthur Benjamin | TEDxOxford
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0:05 - 0:07Good afternoon, ladies and gentlemen,
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0:07 - 0:12my name is Art Benjamin
and I am a "mathemagician". -
0:12 - 0:15What that means
is I combine my loves of math - -
0:15 - 0:17or I should say maths -
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0:17 - 0:21and magic to do what I call "mathemagics".
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0:21 - 0:22But before I get started,
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0:22 - 0:24I've got a quick question
for the audience. -
0:24 - 0:28By any chance, did anyone
here in the audience -
0:28 - 0:32happen to bring with them
this afternoon a calculator? -
0:32 - 0:35If you have one, perhaps
on your phone, or somewhere, -
0:35 - 0:38and you're pretty comfortable
using it, raise your hand. -
0:38 - 0:40I'll need a couple of people
to help me out here. -
0:40 - 0:45I see one... two...
and perhaps one more... three. -
0:45 - 0:49With the three of you, bring out your
calculators and join me up here on stage, -
0:49 - 0:51and let's give these volunteers
a nice round of applause. -
0:51 - 0:52Come on up.
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0:52 - 0:55(Applause)
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0:55 - 0:56Great.
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0:56 - 0:59Over on this side, please.
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1:00 - 1:01Awesome.
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1:01 - 1:04Since I have not had the chance
to work with these calculators, -
1:04 - 1:08I need to make sure
that they are all working properly. -
1:08 - 1:12Would somebody get us started
by giving us a two-digit number, please? -
1:12 - 1:14How about a two-digit number?
Just yell one out. -
1:14 - 1:15Audience: 74.
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1:15 - 1:17Arthur Benjamin: Oh, okay. That's fine! 74
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1:17 - 1:20And another... how about
another two-digit number? -
1:20 - 1:21How about on this side?
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1:21 - 1:22Audience: 39.
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1:22 - 1:25AB: 39. Multiply 74 times 39
on the calculator. -
1:25 - 1:29Make sure you get 2,886,
or the calculators are not working. -
1:29 - 1:32Do each of you get 2,886?
Give them a round of applause! -
1:32 - 1:33(Sighs)
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1:33 - 1:36(Applause)
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1:37 - 1:41I noticed that took some of us
a little bit of time to get the answer. -
1:41 - 1:42That's ok.
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1:42 - 1:46I'll give you a shortcut for multiplying
even faster on the calculator. -
1:46 - 1:49There's something called
"the square of a number" -
1:49 - 1:51which most of you know is taking a number
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1:51 - 1:53and multiplying it by itself.
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1:53 - 1:56For instance 5 squared would be...
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1:56 - 1:5725.
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1:57 - 1:586 squared would be...
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1:58 - 1:5936.
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1:59 - 2:0073 squared would be...
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2:00 - 2:01something else. Yeah.
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2:01 - 2:02(Laughter)
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2:02 - 2:05On most of these calculators,
they've little shortcut buttons -
2:05 - 2:07that allow you to square
numbers even faster. -
2:07 - 2:10What I'm going to try
and do is to square - -
2:10 - 2:13and you might test it - make sure
you could square 5 or 6 with it, -
2:13 - 2:14but what I'm going to try and do
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2:14 - 2:17is to square in my head,
three two-digit numbers -
2:17 - 2:20faster than they can do
on their calculators, -
2:20 - 2:21even using the shortcut method.
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2:21 - 2:25But I'll ask these three people
in the third row - one, two, three. -
2:25 - 2:26Each yell out a two-digit number,
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2:26 - 2:30and if you would square the first one,
the second, and the third one, -
2:30 - 2:32I will try and race you to the answer.
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2:32 - 2:34So quickly a two-digit number, please?
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2:34 - 2:35Audience: 24.
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2:35 - 2:37Arthur Benjamin: 24, great, next...
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2:37 - 2:38What was that?
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2:38 - 2:39Audience: 98.
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2:39 - 2:40AB: 98... and one more...
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2:40 - 2:42Audience: 26.
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2:42 - 2:45AB: 26. Would you call out
your answers, please? -
2:45 - 2:46First volunteer: 576.
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2:46 - 2:47AB: 576.
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2:47 - 2:49Second volunteer: 9,604.
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2:49 - 2:49AB: 9,604.
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2:49 - 2:51Third volunteer: 676.
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2:51 - 2:52AB: 676.
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2:52 - 2:54Give them a round of applause!
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2:54 - 2:57(Applause)
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2:58 - 3:01Let me try to take this one step further.
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3:01 - 3:04I'm going to try to square
some three-digit numbers. -
3:04 - 3:07This time, I won't even write these down.
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3:07 - 3:09I'll just call them out
as they're called out to me. -
3:09 - 3:12Anyone at all call out
a three-digit number, -
3:12 - 3:15anyone on our panel verify the answer.
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3:15 - 3:17If I get the answer right,
give me a big thumbs up. -
3:17 - 3:20If I make a mistake,
let me know, and I'll try and fix it. -
3:20 - 3:22A three-digit number, anyone?
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3:22 - 3:23Audience: 576.
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3:23 - 3:27AB: 576 is 331,776?
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3:27 - 3:28Second volunteer: Yes.
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3:28 - 3:29AB: Yes? Good!
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3:29 - 3:33How about another three-digit number,
sir! a three-digit number? -
3:33 - 3:34Audience: 103.
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3:34 - 3:39AB: 103 is 10,609. Way too easy!
Another three-digit number, please? -
3:39 - 3:40Audience: 125.
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3:40 - 3:44AB: 125 is 15,625, but that's 5
to the 6th power, so that was easy too. -
3:44 - 3:47How about another three-digit number, sir?
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3:47 - 3:48Audience: 985.
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3:48 - 3:52AB: 985 is 970,225.
Yes, thumbs up, if it's right. -
3:52 - 3:55One more three-digit number, sir?
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3:55 - 3:57Audience: 926.
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3:57 - 4:01AB: 926 is 857,476?
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4:01 - 4:02Thank you very much.
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4:02 - 4:03(Applause)
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4:03 - 4:04(Sighs)
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4:04 - 4:07(Applause)
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4:09 - 4:13Let me try to take this one step further.
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4:13 - 4:18I am going to try to square
a four-digit number this time, -
4:18 - 4:20I am not going to beat you
to the answer on this one, -
4:20 - 4:22but I will try to get the answer right.
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4:22 - 4:24To make this a little bit more random,
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4:24 - 4:26how about we use
the fourth row, four people. -
4:26 - 4:30Each of you calls out a single-digit
number between zero and nine, -
4:30 - 4:32that will be a four-digit number
that I will square. -
4:32 - 4:37One, Five, Seven, Seven.
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4:37 - 4:421, 5, 7, 7, this will take me
a little bit of time, so bear with me - -
4:42 - 4:433 million -
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4:45 - 4:46(Sighs)
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4:46 - 4:48(Laughter)
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4:49 - 4:53486,929?
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4:53 - 4:56No? OK, don’t tell me.
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4:56 - 5:03The number was 1, 5, 7, 7. Oh, wait!
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5:03 - 5:053 million - so far so good?
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5:05 - 5:07Oh, is that were I went wrong?
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5:07 - 5:11I never make a mistake, wait.
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5:11 - 5:14Oh. 2 million, was everything else right?
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5:14 - 5:15Volunteer: Yes!
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5:15 - 5:16AB: Thank you very much.
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5:16 - 5:18(Laughter)
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5:18 - 5:19What's one million off? That's all I ask.
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5:19 - 5:21(Applause)
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5:22 - 5:26Now I would attempt to square
a five-digit number, and I can. -
5:26 - 5:30But unfortunately,
most calculators cannot. -
5:30 - 5:33So, since we have reached
the limits of our calculators, -
5:33 - 5:35although some of yours may go higher,
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5:35 - 5:38I'm going to try to conclude
the first part of my show, -
5:38 - 5:40by trying something even trickier.
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5:40 - 5:44Let's take the first number
on the board here: 576. -
5:44 - 5:47Would you each enter 576
on your calculator? -
5:47 - 5:51And instead of squaring it this time,
I'd like you to take that number -
5:51 - 5:55and multiply it by any
four-digit number that you want. -
5:55 - 5:58But don't make it too easy
like 1,000 or 1234, -
5:58 - 6:01but just some random four-digit number.
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6:01 - 6:03So you should have as an answer
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6:03 - 6:07either a six-digit or possibly
a seven-digit number. -
6:07 - 6:10How many digits are on your answer,
six or seven digits? -
6:10 - 6:11Seven.
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6:11 - 6:12Seven.
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6:12 - 6:13Six.
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6:13 - 6:16Is there any possible way
that I could know -
6:16 - 6:19what six or seven-digit numbers
they have? Say "No". -
6:19 - 6:20Audience: No.
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6:20 - 6:21AB: Good.
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6:21 - 6:26Then I shall attempt the impossible,
or at least the improbable. -
6:26 - 6:29What I'd like each of you to do
is to call out for me -
6:29 - 6:32any six of your seven digits,
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6:32 - 6:35or in your case five of your six digits
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6:35 - 6:38in any order you do like.
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6:38 - 6:43One digit at a time, I shall try
and determine the digit you've left out. -
6:43 - 6:48So starting with your six-digit number,
call out any five of them please. -
6:48 - 6:51First volunteer: 8, 0, 9, 3, 8.
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6:51 - 6:55AB: 8, 0, 9, 3, 8,
did you leave out the number 8? -
6:55 - 6:58Yes, that is one.
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6:58 - 7:02You have got seven-digit number.
Call out any six of yours, loud and clear. -
7:02 - 7:06Second volunteer: 4, 7, 2, 5, 8, 4.
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7:06 - 7:08AB: Did you leave out the number six?
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7:08 - 7:10AB: That's two.
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7:10 - 7:13The odds of me getting all three
of these right by pure guessing -
7:13 - 7:15would be one in 1,000:
10 to the third power. -
7:15 - 7:18OK, any six of your digits.
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7:18 - 7:20Really scramble them up this time.
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7:20 - 7:23Third volunteer: 9, 4, 4, 5, 4, 4.
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7:23 - 7:25AB: Did you also leave out the number six?
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7:25 - 7:26Volunteer: Yes.
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7:26 - 7:30AB: Great, and let's give all three
of these people a nice round of applause. -
7:30 - 7:31Thank you very much.
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7:31 - 7:33(Applause).
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7:38 - 7:40For my next number...
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7:40 - 7:42(Laughter)
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7:42 - 7:44I have another question for the audience.
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7:44 - 7:49By any chance, does anyone
here happen to know -
7:49 - 7:54the day of the week
that they were born on? -
7:54 - 7:59If you think you know your
actual birthday, raise your hand. -
7:59 - 8:02Starting with you. What year if I may?
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8:02 - 8:03Audience: 1992.
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8:03 - 8:05AB: 1992, and what month?
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8:05 - 8:05Audience: July.
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8:05 - 8:06AB: July what?
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8:06 - 8:083rd. Was that a Friday?
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8:08 - 8:09Audience: Yes.
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8:09 - 8:10AB: Yes, excellent.
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8:10 - 8:12Somebody else? Yes sir, green shirt.
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8:12 - 8:13What year?
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8:13 - 8:13Audience: 1992
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8:13 - 8:15AB: 1992, and the month?
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8:15 - 8:16Audience: June.
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8:16 - 8:17AB: June what?
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8:17 - 8:18Audience: 30th.
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8:18 - 8:19AB: A Tuesday?
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8:19 - 8:20Audience: Yes.
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8:20 - 8:23AB: Excellent. Somebody else,
how about you? What year? -
8:23 - 8:24Audience: 1995.
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8:24 - 8:26AB: I am sorry sir, what year was it?
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8:26 - 8:27Audience: 1995.
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8:27 - 8:29AB: 1995 and what month?
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8:29 - 8:30Audience: June.
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8:30 - 8:31AB: June what?
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8:31 - 8:32Audience: 26th.
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8:32 - 8:33AB: 26th. Was that a Monday?
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8:33 - 8:34Audience: Yes.
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8:34 - 8:38AB: Excellent. I see a hand up
in the balcony, a young lady. -
8:38 - 8:40I'll try something different here.
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8:40 - 8:45If you are sure of your birthday,
what year was it? -
8:45 - 8:48What day of the week was it?
Tell me in advance the day of the week. -
8:48 - 8:49Audience: Thursday.
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8:49 - 8:53
AB: Thursday. Ok, and what year was it? -
8:53 - 8:54Audience: 2002.
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8:54 - 8:58AB: 2002. Did it happen to be on May 2nd?
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8:58 - 8:58Audience: Yes.
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8:58 - 9:01AB: Yes, but that is my daughter,
I knew that one. -
9:01 - 9:02(Laughter)
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9:02 - 9:06I was there for that, on that Thursday.
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9:07 - 9:12Anyway, I never tried that before.
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9:12 - 9:16Do we have anybody here who doesn't know
the day of the week they were born on -
9:16 - 9:17but would like to find out?
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9:17 - 9:20Ok, now let's see. I'll see yours.
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9:20 - 9:23Now, of course, if you don't know
what it is, I could just make up an answer -
9:23 - 9:25and you will probably believe me.
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9:25 - 9:29But I don't want you to have to do that,
so I come prepared for that situation. -
9:29 - 9:33There is an app for everything these days.
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9:33 - 9:36So, I'll ask one of you here just
to take this and... -
9:36 - 9:41So give us your year and then
type in the year in that blank box. -
9:41 - 9:42What year?
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9:42 - 9:43Audience: 1995.
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9:43 - 9:46AB: 1995. So type in 1995. Great.
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9:46 - 9:47And what month?
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9:47 - 9:48Audience: September.
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9:48 - 9:51AB: September.
Press the September button there. -
9:51 - 9:53And that should give you the calendar.
September what? -
9:53 - 9:54Audience: 21st.
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9:54 - 9:57AB: 21st. I believe, it was a Thursday.
Can we get confirmation? -
9:57 - 9:59It was Thursday. Good.
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9:59 - 10:00I'll tell you what,
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10:00 - 10:02you know since you have the app with you,
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10:02 - 10:04let's try something trickier.
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10:06 - 10:10The app actually goes as far into
the future as 3000, -
10:10 - 10:13as far back into the past as 1600.
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10:13 - 10:15Don't go below 1600.
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10:15 - 10:18Then we get off the Gregorian calendar
and that messes me up a little. -
10:18 - 10:19(Laughter)
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10:19 - 10:21So, what year would you like?
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10:21 - 10:25Choose a year between
1600 and 3000. Go ahead. -
10:25 - 10:27Audience: 2730.
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10:27 - 10:35AB: 2730. So enter 2730 into that.
And what month would you like? -
10:35 - 10:36Audience: June.
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10:36 - 10:37AB: June what?
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10:37 - 10:39Audience: 13th.
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10:39 - 10:42AB: 13, will that be a Friday?
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10:42 - 10:43Audience: Yes.
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10:43 - 10:46AB: Yes, and it'll be cloudy
on that day too If I am not mistaken. -
10:46 - 10:47Thank you very much.
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10:47 - 10:49(Applause)
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10:54 - 10:57In fact, anybody else who wants
to find out their birthday, -
10:57 - 11:01see me in the lobby, perhaps in the break,
I'll be more than happy to tell you. -
11:01 - 11:05Now, just a little bit of time left
so I'd like to do one last thing for you -
11:05 - 11:09that I alluded to earlier when we had
the other calculators on stage. -
11:09 - 11:13I am going to try to square
a five-digit number, -
11:13 - 11:17requiring if you have a ten-digit
calculator or higher. -
11:17 - 11:20Fell free to bring out your
calculator at this point. -
11:20 - 11:26But to make my job more interesting
for you as well as for me, -
11:26 - 11:31I going to do this last problem
thinking out loud, -
11:31 - 11:34so you can actually honestly hear
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11:34 - 11:36what is going on in my mind,
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11:36 - 11:39while I do a calculation of this size.
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11:39 - 11:42Let's create a five-digit number.
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11:42 - 11:43Why we just go up to this aisle,
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11:43 - 11:47the first five people along the aisle,
each gives me a single-digit, -
11:47 - 11:50that will be my five-digit number.
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11:50 - 11:52Three.
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11:52 - 11:54Seven.
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11:54 - 11:55Six.
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11:55 - 11:58Nine.
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11:58 - 11:59One.
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11:59 - 12:0737,691 squared. Yuck!
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12:07 - 12:11Let me explain to you how
I'm going to attempt this problem. -
12:11 - 12:14I'm going to break the problem down
into three parts. -
12:14 - 12:17I'll do 37,000 squared,
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12:17 - 12:20plus, 691 squared,
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12:20 - 12:26plus, 37,000 times 691 times 2.
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12:26 - 12:32Add all those numbers together
and with any luck arrive at the answer. -
12:32 - 12:33Now, let me explain one more thing.
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12:33 - 12:41While I do this calculation you might hear
certain words, as opposed to numbers, -
12:41 - 12:42creep into the calculation.
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12:42 - 12:44Let me explain what that is.
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12:44 - 12:49This is a phonetic code,
a mnemonic device that I use, -
12:49 - 12:52that allows me to convert
numbers into words. -
12:52 - 12:56I store them as words, and later on
retrieve them as numbers. -
12:56 - 12:58I know it sounds complicated, it's not.
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12:58 - 13:00I just don't want you to think,
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13:00 - 13:02you're seeing something
out of "Rain Man" here. -
13:02 - 13:03(Laughter)
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13:03 - 13:05There's definitely
a method to my madness - -
13:05 - 13:07definitely, definitely. Sorry.
-
13:07 - 13:09(Laughter)
-
13:09 - 13:12One last instruction
for my judges with calculators. -
13:12 - 13:15Now who has got an answer
in front, raise your hand. -
13:15 - 13:16Okay, enough of you.
-
13:16 - 13:21There is a 50% chance that I will make
a mistake on this problem. -
13:21 - 13:24If I do, don't tell me
what the mistake is, -
13:24 - 13:27just say, "You're close or something,"
-
13:27 - 13:30and I'll try and figure it out which
could be pretty entertaining in itself. -
13:30 - 13:33If, however, I am right, whatever you do,
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13:33 - 13:35don't keep it to yourselves.
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13:35 - 13:38Make sure everybody knows
that I got the answer right, -
13:38 - 13:40because this is my big finish, OK?
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13:40 - 13:43So, without any more stalling,
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13:43 - 13:46here we go.
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13:46 - 13:49I'll start the problem in the middle,
with 37 times 691. -
13:49 - 13:51Now, let's see - Oh my gosh -
so that is 700 minus 9 -
13:51 - 13:54I will take advantage on that,
700 times 37 is 25,900. -
13:54 - 13:5937 times 9 is 333, subtract
the two to get 25,567. -
13:59 - 14:0625,000 - do I believe that, yeah -
25,567 double that to get 51,134. -
14:06 - 14:15- 51,134 OK - 51,000 becomes
late tomorrow, late tomorrow is 51,134. -
14:15 - 14:16That seems right, I'll go on.
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14:16 - 14:22Next, I do 37 squared which is 1,369,
so I can say 1 billion. -
14:22 - 14:25Take the 369 add that to light.
Is there going to be ??? -
14:25 - 14:31369 add that to light to get 420 million.
Tomorrow, tomorrow, OK. -
14:31 - 14:37Next, we do 691 squared that 700 times
682, plus 9 squared that is 477,481. -
14:37 - 14:40Raft, if I need it, raft, take the 477,
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14:40 - 14:46add that to tomorrow to get 611,481?
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14:46 - 14:47Audience: Yeah!
(Applause). -
14:47 - 14:49AB: Yes, good.
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14:49 - 14:51Thank you all very much.
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14:51 - 14:55I hope you enjoyed mathemagics.
I am Arthur Benjamin. Thank you. -
14:55 - 14:58(Applause)
- Title:
- Faster than a calculator | Arthur Benjamin | TEDxOxford
- Description:
-
Benjamin makes numbers dance. In his day job, he's a professor of mathematics at Harvey Mudd College; in his other day job, he's a "Mathemagician," taking the stage to perform high-speed mental calculations, memorisations and other astounding mathematic stunts. It's part of his drive to teach math and mental agility in interesting ways, following in the footsteps of such heroes as Martin Gardner.
This talk was given at a TEDx event using the TED conference format but independently organized by a local community. Learn more at http://ted.com/tedx - Video Language:
- English
- Team:
- closed TED
- Project:
- TEDxTalks
- Duration:
- 15:05
Rhonda Jacobs edited English subtitles for Faster than a calculator | Arthur Benjamin | TEDxOxford | ||
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Nadine Hennig accepted English subtitles for Faster than a calculator | Arthur Benjamin | TEDxOxford | ||
Nadine Hennig edited English subtitles for Faster than a calculator | Arthur Benjamin | TEDxOxford | ||
Nadine Hennig edited English subtitles for Faster than a calculator | Arthur Benjamin | TEDxOxford | ||
Nadine Hennig edited English subtitles for Faster than a calculator | Arthur Benjamin | TEDxOxford | ||
Mohammed Basheer edited English subtitles for Faster than a calculator | Arthur Benjamin | TEDxOxford |