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Struggling with the nine times table? I have a failsafe method (www.theguardian.com)
submitted 3 months ago by to c/nottheonion@lemmy.world
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Apparently, nines are the hardest to grasp for primary school children. If only they’d learned how to cheat like me, says Adrian Chiles

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[–] 8 points 3 months ago (9 children)

"Cheats" like this is why critical thinking is fucked...

Kids are supposed to learn:

Times 10 adds a zero, minus one from that is times 9

And different steps for different rows/columns.

We shouldn't "memorize" the times tables, because that's just memorization. These cheats learn a process, but it dead ends at this, it can't be used as a foundation to build on the real skill it should be developing: doing multiple math steps in your head.

If done right it "times tables" are the most important building block in being good at math. But for decades teachers just care if the right answer is spit out.

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  • [–] 10 points 3 months ago*

    I use my memorized times tables in my head a lot more often than many other math skills. But maybe I'm just weird, I'm certainly no math whiz. Yet.

    Edit: I realize this may just be because I don't have many other math skills, to your point.

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  • [–] 8 points 3 months ago

    We shouldn't "memorize" the times tables,

    While I agree with your sentiment, times table memorization is necessary to build a skill that will be needed later in math. It's good to teach the basis of the times table but if you don't have it memorized, every later math problem will be slower to solve because you will be focusing on the principles of how a times table works instead of the new concept like how to multiply long number with carry.

    This is related to my pet peeve, that despite it being 40 years ago is still burned into my memory. I had many Physics professors who would talk about not needing to memorize formulas for exams because they could be derived from first principles. Those same professors were always the ones who would give exams that if you didn't have formulas memorized, there wouldn't be time to finish.

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  • [–] 2 points 3 months ago* (last edited 3 months ago) (1 child)

    I agree the the number-theoretic shortcuts for multiplication (and division!) based on the factors of 9, 10, and 11 should be taught.

    I disagree that single-digit sums and products shouldn't be memorized. Neither students nor practitioners derive formulae from first principles each and every time, and breaking down a single-digit sum or product into "simpler" ones is a very similar ask.

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  • [–] 3 points 3 months ago

    Neither students nor practitioners derive formulae from first principles each and every time,

    1. If they have it memorized, it's from years of usage, they didn't need to practice moroizing the things theyd use every day. Because it would happen anyways.

    2. Math class isn't applied Math, it's just Math. Giving credit for memorizing someone else's equation is a way to push people thru who can't do the math.

    And even in a hypothetical world where someone needs to apply an existing mathematical formula that they don't use constantly, they're not gonna just risk it to save 2 seconds checking.

    I understand why you have the opinion you have, but that doesn't mean our education system was blinded in the pursuit of metrics generations ago, hell, it's ancedotal evidence it did...

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  • [–] 1 point 3 months ago (1 child)

    If you try to do that for all multiplication you might end up with something like 10*6 = 60 - 6 = 54 - 6 = 48 - 6 = 42 - 6 = 36 and even then the subtractions are going to involve some memorization unless you are counting down or something.

    You kinda need to have the basic operations involving the 10 digits in our common number system memorized to then start building algorithms for more complicated problems like multi digit numbers.

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  • [–] -2 points 3 months ago*

    you might end up with something

    Literally the point I was trying to get thru to people.

    The thing is there's a lot of human variation, and if I wrote it out enough for everyone to understand, no one would read it.

    So I end up with shit like your reply.

    You don't understand the goal, so you don't understand why it's being taught

    And after (maybe) reading the other comments, you come in completely sincerely with "just memorize it".

    I know you're trying to help, and legitimately don't see the problem here. But fucking come on man, at least ask questions and people may explain it

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  • [–] 0 points 3 months ago (2 children)

    This seems utterly detached from reality. From experience the theory behind times tables are taught at length then the tables are memorised for quick recall during utilisation.

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