This post reminded me of this question.
I grew up in the 80s. I took math all through primary education and through two years college math (Calc 1, Calc 2, DiffEq, something else I don’t remember). I don’t ever really remember using sets very much, if at all.
What is the purpose of trying to teach it to kids in 3rd grade? Does it actually help them in their standard math education?
I am not saying it won’t or can’t, I am just not seeing a lot of utility. Please educate me.
Who is trying to teach 3rd graders set theory? The post you linked only mentions one set theory piece of notation.
My daughter’s curriculum had it.
I’m pretty much mathematically illiterate, and have the high school transcripts to prove it. Set theory is pretty much the ONLY part of post-arithmetic math I understood.*
*I believe I also learned that the sum of all the interior angles of a polygon can’t exceed 360 degrees, but I’d need to look that up.
Things like subsets, unions, and intersections come up a lot in everyday life (whether or not you use those specific words for them).
It appears our educational system has failed you: a pentagon is a polygon with an interior angle of 108 degrees, which, *5, adds up to 540 degrees. Sorry.
Exterior. But close.
Is this the level of set theory being taught to 3rd graders? That’s perfectly reasonable. Set theory comes up in elementary school all the time as kids are formed into groups for educational purposes or just playing at recess*.
*Kids still have recess and are allowed to play right?
Yeah, set theory strikes me as one of the branches of math that’s fairly useful in the real world to most people. Certainly far more useful than what seems like a whole year we spent in elementary school proving various properties of triangles, nearly all of which was immediately obsolete when we got to algebra because they basically all reduce to something you can solve with the Pythagorean theorem and the quadratic formula.
Set theory is a useful precursor to logic and algorithms, so it might be a good idea to introduce it early if you want your kids to be able to code.
True, and it’s something that doesn’t require multiplication or division. It’s probably good to get them thinking in those terms for things like civics, grammar, geography, science. Plus Alice in Wonderland.
Presumably taught using Venn/Euler diagrams so it’s pretty kid-friendly.
Exterior angle of a pentagon is 252. *5 = 1260. I recommend joining Kent Clark for some remedial geometry study.
Don’t understand this post at all. Anyway, the sum of the exterior angles of any convex (that’s an important qualification) polygon is exactly 360 deg. Think of it this way. The exterior angle at a vertex is the angle you have to turn through to get from one edge to the next, assuming it is convex. To get all the way round the polygon you have to turn through 360. When the polygon isn’t convex an extended side goes into the polygon and the “exterior angle” is interior and should be subtracted.
As for the OP, I think set theory is a welcome and easy respite from too many long division problems which is what turns many people off from math. Anyway, the study of Hermitian operators has to start with set theory, which I assume you know.
By “exterior angle,” I think that the poster meant the supplements of the interior angles.
To the OP, I have used set theory in database programming.
I don’t know where you guys learned your geometry, but this is just completely wrong and you can see that it’s wrong just by sketching a polygon on a piece of paper and roughly estimating angles; the bit about ‘to get all the way around the polygon you have to turn through 360’ is just incorrect. This page has a polygon diagram that you can play around with to see how it works. Convex Polygon Definition - Math Open Reference
Note that since a convex polygon is one in which all of the interior angles are less than 180 degrees, that means that all of the exterior angles are greater than 180 degrees as the interior and exterior measure of an angle at a point always sums to 360 degrees. Which means that the sum of any two exterior angles on a convex polygon is greater than 360 degrees.
Nope, the interior and exterior angles sum to 180 degrees. “Exterior angle” has a specific meaning, and it doesn’t mean what you think it means.
I’m not sure how two people could fail to understand that to the point that they would question others geometry skills.
Maybe that’s why my bookshelves never seem to fit together. :smack:
Maybe we could institute remedial geometry classes for adults, and leave the kids to get on with “Fish are animals, but not all animals are fish” and suchlike. 
I first was taught set theory as a part of th New Math in 1965, so it was obviously taught us so we could beat the Russkies. Duh!
My first database class some thirty years later triggered a “I know this shit!” moment. Which put me ahead of my classmates. My parents ’ investment in my parochial education finally paid off. :dubious: