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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