[HN Gopher] The Party Math Trick
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The Party Math Trick
Author : bern4444
Score : 39 points
Date : 2021-11-28 06:31 UTC (2 days ago)
(HTM) web link (sambernheim.com)
(TXT) w3m dump (sambernheim.com)
| joenot443 wrote:
| Yeah, I donno. Even if I were able to convince someone at a party
| to go along with this "trick", I don't think they'd be especially
| impressed when after scrambling and subtracting 4 digit numbers,
| I'm able to wow them with a single digit.
| Supermancho wrote:
| I picked 5000. The trick doesn't work and demonstrably, the
| automated version doesn't know what number I picked.
|
| A different issue by picking 2222 (anything that ends up with all
| 0s or 9s ofc)
|
| Not something I would bring up at a party because people are
| drinking and not really interested in doing addition/subtraction
| and will DEFINITELY pick simple numbers. By the time you get into
| "it has to be non-zero digits" they have already become bored.
|
| It feels like my little brother running up to me and screaming
| "What's 729 squared?" and without a beat "531,441" , "I'm smarter
| than you!"
| pkulak wrote:
| 345 also doesn't work if you pick 435 as the shuffle, for
| example.
| tgb wrote:
| Your example does work for this.
| Supermancho wrote:
| Corrected.
| karaterobot wrote:
| How this goes in real life:
|
| "Was your number... 3741?"
|
| "No."
|
| "Heh, I'm afraid that's impossible based on number theory. You
| must have made a mistake in the step where I asked you to choose
| a second 4-digit number by scrambling the four digits of the
| first number and subtracting the larger number from the smaller.
| Try it again, I'll wait."
|
| "No."
| whatshisface wrote:
| A good magician would ask them to have a calculator out... or
| present only to an audience of geniuses.
| auggierose wrote:
| Watch "Last year at Marienbad" for the ultimate math party game
| :-)
| m_st wrote:
| Oh thanks for getting me spending about an hour on Wikipedia
| reading about this movie, the relation to Godard movies, and so
| much else :-) Will definitely watch this one soon!
| Jun8 wrote:
| Here's a _much_ better party /bar trick: 1. Point
| to the drink glass in front of you 2. Ask friend if they
| think the circumference or height of the glass is larger 3.
| Friend will invariably think that height is larger 4. Wager
| for a drink that that's not the case 5. Use a straw to
| measure the circumference and then height 6. Enjoy your
| free drink
|
| Unless you've picked an a Champaigne flute you'll always win. To
| make it even more fun, for (4) wager that the circumference will
| be _two_ times the height to make it sound more incredulous. For
| typical glasses you may go up to three!
|
| I learned this trick from _Things to Make and Do in the Fourth
| Dimension_ (https://www.amazon.com/Things-Make-Fourth-Dimension-
| Mathemat...), overall good book.
| thehappypm wrote:
| This guy must go to parties with Good Will Hunting.
| jrumbut wrote:
| When he said "now subtract the two 4 digit numbers" I felt a
| whole room full of eyes glaze over.
| sumtechguy wrote:
| That sort of trick is a terrible opener. You want something
| simple for an opener. A 'tweener' trick yeah something like
| this is OK, but read your audience. I may have binge watched
| all of scam school.
| localhost wrote:
| When I was a kid, I loved the Mathemagic book [1] IIRC this was
| one of the tricks described in the book.
|
| [1] https://www.amazon.com/Mathemagic-Raymond-Blum/dp/0806983558
| leecarraher wrote:
| some python to do this trick and find counterexamples that won't
| work import random as r def fnc(b):
| bstr = list(str(b)) if bstr.count(bstr[0]) ==
| len(bstr): return "can't shuffle"
| max_ct = len(bstr)*10 # do while
| r.shuffle(bstr) b_shuf = int(''.join(bstr))
| diff = abs(b-b_shuf) bstr = list(str(diff))
| i = r.randint(0,len(bstr)-1) while bstr[i] ==
| '0' or bstr[i] == '9': i =
| r.randint(0,len(bstr)-1) bstr = list(str(b))
| r.shuffle(bstr) b_shuf = int(''.join(bstr))
| diff = abs(b-b_shuf) bstr = list(str(diff))
| max_ct -=1 if max_ct == 0:
| return "bollocks!" del(bstr[i])
| s = sum(map(int,bstr)) i =0 while (i+s) %
| 9 != 0: i+=1 return bstr,i,diff
| j7ake wrote:
| I would bet a decent chunk of money the author has never
| successfully tried this at a party.
|
| Asking people to subtract two 4 digit numbers and picking digits
| that are not 0 and 9 is absolutely not a "party trick".
| Keyframe wrote:
| Maybe title would have to be The Math Party Math Trick.
| icameron wrote:
| I'm being honest here. Reading along I randomly picked 987 from
| my brain. I scrambled that to 897. Subtracting the smaller from
| the larger I got 90, per the instructions. So I am unable to tell
| you the remaining digits starting with a number that isn't 9 or
| 0.... Maybe I'm a "you must be fun to talk to at parties" kind of
| guy.
| cphoover wrote:
| lol
| coldpie wrote:
| I did the same thing, starting from 100. I guess maybe "no
| digits" is a sufficient response to end up with 90?
| leecarraher wrote:
| yeah for first 10000 digits there is about a 2%-5% chance
| (around 20%-5% for first 2k, then falls below 2% for remaining
| 2/3s) of selecting one that doesn't work. obviously picking
| something like 1111, 2222, ... won't work either since you
| can't rearrange it to anything but 0s.
| kej wrote:
| Although not mentioned in the article, the trick can handle
| this. The rule should be "remove a digit that isn't 0", and if
| the sum of remaining digits is divisible by 9 then the removed
| digit must be 9 as well. That will cover everything except the
| case when the original number and the scrambled number are the
| same.
| clashmoore wrote:
| Back in grade school when playing with a calculator, I came
| across this weird pattern when adding various combinations of 3
| digit numbers on the number pad.
|
| I wonder if there is something similar at foot as with this
| trick.
|
| As follows, taking a calculator and the number grid, so a series
| of additions of a row added to the reverse of that row added to
| the second row, etc etc.
|
| So following a horizontal pattern: 123 + 321 + 456 + 654 + 789 +
| 987 = 3,330
|
| Now, let's see the sum when we use a vertical pattern: 147 + 741
| + 258 + 852 + 369 + 963 = 3,330
|
| Then, you can also do the diagonals:
|
| Diagonally NW to SE: 748 + 847 + 159 + 951 + 263 + 362 = 3,330
|
| Second Diagonal NW to SE: 784 + 487 + 159 + 951 + 623 + 326 =
| 3,330
|
| Diagonally SW to NE: 142 + 241 + 753 + 357 + 869 + 968 = 3,330
|
| Second Diagonally SW to NE: 421 + 124 + 753 + 357 + 689 + 986 =
| 3,330
|
| Just a silly occurrence that they all sum to the same value
| 3,330.
| kazinator wrote:
| Notice that in this arrangement 1 2 3 4 5
| 6 7 8 9
|
| opposite values add up to 10: 1 + 9, 2 + 8, 3 + 7, 4 + 6. This
| has to do with why the last digit of the sums you are seeing is
| always 0: 3330.
|
| For instance in 123 + 321 + 456 + 654 + 789 + 987, the last
| digit is (3 + 1) + (6 + 4) + (9 + 7). We can rearrange these
| six numbers into (1 + 9) + (4 + 6) + (7 + 3) = 10 + 10 + 30 =
| 30.
|
| Ok, so now we have a 0, and a carry of 3.
|
| Next, note that since the diagonally opposite elements add to
| 10, all the three-element traces that pass through the center 5
| necessarily add up to 15: (1 + 5 + 9) = (2 + 5 + 8) = (3 + 5 +
| 7) = (4 + 5 + 6) = 15.
|
| In calculating the second digit of the sum you have 2 5 and 8,
| which occur twice: (2 + 2 + 5 + 5 + 8 + 8) = 30. Combine that
| with the carried 3 and you get 33. Put down the 3 and carry the
| 3.
|
| Then again, the 100's digit is just mirror image of the ones:
| it adds up to 30, which combines with the carried 3 to make 33.
|
| With 784 + 487 + 159 + 951 + 623 + 326, though you have
| rearranged the digits to form corner triangles, that is just a
| red herring. If you look at the ones digits inside this sum,
| you have 4 7 9 1 3 6. These is just the set made up of the left
| and right columns of the square, which we know can be put into
| 3 pairs adding to 10, making 30. Again we get our 0 to put down
| and 3 to carry.
|
| The middle digits, the tens, are once again 8 5 and 2, doubled
| up again: another 15 x 2 = 30: put down 3, carry 3.
|
| And so it goes.
| davchana wrote:
| It stays true for digits 1,3,7,9 i.e. 13+31+79+97 = 17+71+39+93
|
| also for 1,2,4,5 with 12+21+45+54 = 14+41+25+52
|
| Maybe there is some pattern.
|
| Something similar we used to do in school to find answers for
| multiplication table of 9. We used to write all tables from 1
| to 20, recite & them read them back from memory.
|
| We would go by writing 9, ten times in ten total rows, like
|
| 9 9 .... 9
|
| Then from tenth row come up by writing x (sign of
| multiplication)
|
| 9x
|
| Now go down again writing 1,2,3 in each row like
|
| 9x1 9x2 .... 9x10
|
| Now come up writing = in every row.
|
| Now go down writing digits 0 to 9 like
|
| 9x1=0 9x2=1 .... 9x10=9
|
| Now write 0 to 9 again going up, ending up with table.
|
| 9x1=09 9x2=18 9x3=27 ..... 9x10=90
| dragontamer wrote:
| Actual Math Party tricks are standard affairs: just jokes about
| Math.
|
| * "Hey Babe, would you like to be my derivative and lie tangent
| to my curves?"
|
| * Question: What did Euler discover while sitting on the toilet?
|
| -- Answer: A natural log.
|
| * Question: Why do programmers mix up Christmas and Halloween?
|
| -- Answer: Because Dec(imal) 25 == Oct(al) 31.
|
| * Once upon a time, a big, evil derivative was approaching town.
| All the polynomials ran away in terror, expecting themselves to
| be derived away. Suddenly, the local Sheriff appeared, and rode
| out to parley with the derivative.
|
| The Sheriff and Derivative meet up, and a showdown was about to
| occur. Knowing that it will all be over soon, they exchanged
| pleasantries before the final showdown.
|
| The Sheriff introduces himself: "I'm e^x, the Sheriff of this
| town. You can't dare to derive me!"
|
| Upon hearing the name: the evil derivative gives a toothy grin
| and says "My name is d/dy".
|
| Etc. etc. Assuming you're comfortable telling these kinds of
| jokes of course. As usual, you need to read the room and see if
| the jokes would fly in the company you're in.
| onychomys wrote:
| Q: What do you get when you cross an hippo and an aardvark?
|
| A: HippoAardvarkSinTheta
|
| Q: What do you get if you cross a mosquito and a mountain
| climber?
|
| A: Nothing, you can't cross a vector and a scalar!
| tzs wrote:
| Q: What's yellow and equivalent to the axiom of choice?
|
| A: Zorn's lemon!
| supernova87a wrote:
| I guess it's a good party trick if you've never been to a good
| party.
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(page generated 2021-11-30 23:01 UTC)