[math-fun] Improving on counting backward from 100 by sevens
I'd like to know the origin of this commonly-deployed cognitive test. It is a nice one I think—the first three stepping stones, 93, 86, and 79—have obscure factorizations, and it's only at 72 where I'm first able to be entirely confident that I haven't screwed it up, since 100-72 is "obviously" 28, which is 7*4. I'm weak at mental arithmetic generally speaking though. Are there any other similarly-mathy tests like this that people use? -- Thane Plambeck tplambeck@gmail.com http://counterwave.com/
Well, I remember my junior high French teacher having us count round-robin in French starting at one. The catch was that for every number that either had a seven in it, or was a multiple of seven, you were supposed to say "attention!" instead of the number. If you made a mistake, or took too long, you were eliminated, until one student was left. Keeping track of where you were when going through the seventies was particular hard. On 21-May-15 12:56, Thane Plambeck wrote:
I'd like to know the origin of this commonly-deployed cognitive test.
It is a nice one I think—the first three stepping stones, 93, 86, and 79—have obscure factorizations, and it's only at 72 where I'm first able to be entirely confident that I haven't screwed it up, since 100-72 is "obviously" 28, which is 7*4. I'm weak at mental arithmetic generally speaking though.
Are there any other similarly-mathy tests like this that people use?
My kids learned a variant of this, where you count round-robin but have to skip over all the numbers that contain a 5. "If you say the number five / you will be disqualified!" Jim Propp On Thu, May 21, 2015 at 1:35 PM, Mike Speciner <ms@alum.mit.edu> wrote:
Well, I remember my junior high French teacher having us count round-robin in French starting at one. The catch was that for every number that either had a seven in it, or was a multiple of seven, you were supposed to say "attention!" instead of the number. If you made a mistake, or took too long, you were eliminated, until one student was left. Keeping track of where you were when going through the seventies was particular hard.
On 21-May-15 12:56, Thane Plambeck wrote:
I'd like to know the origin of this commonly-deployed cognitive test.
It is a nice one I think—the first three stepping stones, 93, 86, and 79—have obscure factorizations, and it's only at 72 where I'm first able to be entirely confident that I haven't screwed it up, since 100-72 is "obviously" 28, which is 7*4. I'm weak at mental arithmetic generally speaking though.
Are there any other similarly-mathy tests like this that people use?
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When I taught in what you would call a grade school, 76 years ago, I used the last 5 mins of each class to play ``fizz-buzz'' :- one,two,three,four,fizz,six,buzz,eight,nine,fizz,eleven,twelve,thirteen, buzz,fizz,sixteen,buzzteen,eighteen,nineteen,fizz,buzz,twentytwo,... thirtyfive was fizzbuzz, etc. It had the advantage that it kept all the class thinking, as those who had dropped out were eager to catch mistakes by those still in ... R. On Thu, 21 May 2015, James Propp wrote:
My kids learned a variant of this, where you count round-robin but have to skip over all the numbers that contain a 5. "If you say the number five / you will be disqualified!"
Jim Propp
On Thu, May 21, 2015 at 1:35 PM, Mike Speciner <ms@alum.mit.edu> wrote:
Well, I remember my junior high French teacher having us count round-robin in French starting at one. The catch was that for every number that either had a seven in it, or was a multiple of seven, you were supposed to say "attention!" instead of the number. If you made a mistake, or took too long, you were eliminated, until one student was left. Keeping track of where you were when going through the seventies was particular hard.
On 21-May-15 12:56, Thane Plambeck wrote:
I'd like to know the origin of this commonly-deployed cognitive test.
It is a nice one I think—the first three stepping stones, 93, 86, and 79—have obscure factorizations, and it's only at 72 where I'm first able to be entirely confident that I haven't screwed it up, since 100-72 is "obviously" 28, which is 7*4. I'm weak at mental arithmetic generally speaking though.
Are there any other similarly-mathy tests like this that people use?
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On Thu, May 21, 2015 at 1:35 PM, Mike Speciner <ms@alum.mit.edu> wrote:
Well, I remember my junior high French teacher having us count round-robin in French starting at one. The catch was that for every number that either had a seven in it, or was a multiple of seven, you were supposed to say "attention!" instead of the number. If you made a mistake, or took too long, you were eliminated, until one student was left. Keeping track of where you were when going through the seventies was particular hard.
Yeah, French numbers 70-99 are strange — combinations of 60 or 80 with 1 through 20 or 19: 70 soixante-dix 71 soixante et onze 72 soixante-douze 73 soixante-treize 74 soixante-quatorze 75 soixante-quinze 76 soixante-seize 77 soixante-dix-sept 78 soixante-dix-huit 79 soixante-dix-neuf 80 quatre-vingts 81 quatre-vingt-un 82 quatre-vingt-deux 83 quatre-vingt-trois 84 quatre-vingt-quatre 85 quatre-vingt-cinq 86 quatre-vingt-six 87 quatre-vingt-sept 88 quatre-vingt-huit 89 quatre-vingt-neuf 90 quatre-vingt-dix 91 quatre-vingt-onze 92 quatre-vingt-douze 93 quatre-vingt-treize 94 quatre-vingt-quatorze 95 quatre-vingt-quinze 96 quatre-vingt-seize 97 quatre-vingt-dix-sept 98 quatre-vingt-dix-huit 99 quatre-vingt-dix-neuf perhaps a macrocosm of how 17-19 don't follow the same pattern as 11-16. ——Dan
On 5/21/2015 1:00 PM, rkg wrote:
When I taught in what you would call a grade school, 76 years ago, I used the last 5 mins of each class to play ``fizz-buzz'' :-
one,two,three,four,fizz,six,buzz,eight,nine,fizz,eleven,twelve,thirteen, buzz,fizz,sixteen,buzzteen,eighteen,nineteen,fizz,buzz,twentytwo,...
thirtyfive was fizzbuzz, etc. It had the advantage that it kept all the class thinking, as those who had dropped out were eager to catch mistakes by those still in ... R.
i wonder if the fizz buzz test <http://c2.com/cgi/wiki?FizzBuzzTest> came from the same place? thanks -- Honesty is a very expensive gift. So, don't expect it from cheap people - Warren Buffett http://tayek.com/
Remarkably few solutions implement the obvious, time-optimal strategy switching on the remainder modulo 3*5 = 15 . Faced with this problem in an interview, my response would be to ask in what proportions the solution was required to optimise time, space, effort, elegance, readability, portability, etc. I wouldn't get the job --- but probably wouldn't want it anyway! WFL On 5/22/15, Ray Tayek <rtayek@ca.rr.com> wrote:
On 5/21/2015 1:00 PM, rkg wrote:
When I taught in what you would call a grade school, 76 years ago, I used the last 5 mins of each class to play ``fizz-buzz'' :-
one,two,three,four,fizz,six,buzz,eight,nine,fizz,eleven,twelve,thirteen, buzz,fizz,sixteen,buzzteen,eighteen,nineteen,fizz,buzz,twentytwo,...
thirtyfive was fizzbuzz, etc. It had the advantage that it kept all the class thinking, as those who had dropped out were eager to catch mistakes by those still in ... R.
i wonder if the fizz buzz test <http://c2.com/cgi/wiki?FizzBuzzTest> came from the same place?
thanks
-- Honesty is a very expensive gift. So, don't expect it from cheap people - Warren Buffett http://tayek.com/
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participants (7)
-
Dan Asimov -
Fred Lunnon -
James Propp -
Mike Speciner -
Ray Tayek -
rkg -
Thane Plambeck