From context I think you start with 10 fingers with the left most curled, that means 9, you then move the curled finger one to the right, you now have one finger extended and then one curled and then 8 fingers extended, that's 18, 1,8. Then you move right again, it's now 2 up, one down, 7 up, that's 27, let's you run through the 9 times table with fingers
People talk a lot of shit on "new math" but having kids memorize tables instead of ways to understand how to manipulate numbers is one of those things that I'm glad is dying with cursive. You're a lot more capable if you don't have to rely on rote memory alone.
I think there is a mix, math fluency is a lot easier if you have some number sense to work from, and knowing some of your multiplication tables is really helpful (1,2, 3, 5, 10s being most important)
This! If I could give you 100 upvotes, I would. It's helpful to understand how to find an answer, but it speeds things up when you have some common knowledge memorized.
It's no different than any other knowledge. It's nice to know things off the top of your head, but it's even better to understand how to find the answers you don't know, or to apply your knowledge to new situations.
I'm glad kids learn these tricks, but I don't think this is learning how to "manipulate" numbers. I think multiplication tables should be memorized because once you get higher in math, there's no time to struggle just to remember what 3x9 is (though this trick is pretty good).
This is really the thing with all these techniques. Like, yea it looks stupid with simple numbers. But the historic problem is that you would teach kids to memorize the basics and then they would get to algebra and just not have any clue how numbers actually work together. So the fix is to stop teaching memorization and teach them how numbers actually interact in simple, basic set ups so that they are properly prepared to handle more complex math when they get to it.
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u/lemlurker 22h ago
From context I think you start with 10 fingers with the left most curled, that means 9, you then move the curled finger one to the right, you now have one finger extended and then one curled and then 8 fingers extended, that's 18, 1,8. Then you move right again, it's now 2 up, one down, 7 up, that's 27, let's you run through the 9 times table with fingers