That's how I usually solve for nines in my head! And yes, some of these things seem like "tricks," but they're just math being awesome. Reminds me of Nix the Tricks.
It came out about 13 years ago as a free online collection by Tina Cardone, and I believe others were invited to contribute to it. Not sure if it still exists in that format, but here's the book version: https://a.co/d/098dpiBs
Please forgive me if I’m wrong, but I would venture a guess that the post you’re planning to write (I think that’s what you mentioned) about multiplying 11 goes something like this. To multiply 34 × 11, you start with 3, then add 3+4, then end with 4 and you get 374. (If so, that’s the Trachtenberg Method). Hope I’m not overstepping the bounds for Substack on this one. :-)
Here’s his book. "The Trachtenberg Speed System of Basic Mathematics" by Jakov Trachtenberg. You can get a used version pretty cheaply on Amazon. I haven’t read this since the 1980’s but it was actually one of the main reasons I got interested in teaching math. And, there’s a really interesting story behind it. I think he wrote most of it while in jail!
Here's another version of this that looks like a trick, but it's actually just "math being math-y" https://www.youtube.com/shorts/SIP0O7i-inc
That's how I usually solve for nines in my head! And yes, some of these things seem like "tricks," but they're just math being awesome. Reminds me of Nix the Tricks.
Do you have a reference for Nix the Tricks?
It came out about 13 years ago as a free online collection by Tina Cardone, and I believe others were invited to contribute to it. Not sure if it still exists in that format, but here's the book version: https://a.co/d/098dpiBs
Thanks. Looks interesting. I ordered it!
I’m guessing you’re probably familiar with the Trachtenberg Method?
I am not! Please tell me about it!
Please forgive me if I’m wrong, but I would venture a guess that the post you’re planning to write (I think that’s what you mentioned) about multiplying 11 goes something like this. To multiply 34 × 11, you start with 3, then add 3+4, then end with 4 and you get 374. (If so, that’s the Trachtenberg Method). Hope I’m not overstepping the bounds for Substack on this one. :-)
Yep, that's it. Does he explain in the book why that works?
Unfortunately, it's been so long ago I don't remember. Sorry,
Here’s his book. "The Trachtenberg Speed System of Basic Mathematics" by Jakov Trachtenberg. You can get a used version pretty cheaply on Amazon. I haven’t read this since the 1980’s but it was actually one of the main reasons I got interested in teaching math. And, there’s a really interesting story behind it. I think he wrote most of it while in jail!