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I thought you give 1 from 7 to 9 so it becomes 10+6 !!
You can do that, too.
A dozen years ago or so there was a huge uproar about “common core” mathematics, which was a new standard being used in the USA for teaching.
It was a politicized trendy topic and even so-called-intellectuals were jumping on the train and calling it a deranged way of learning math.
I looked into it a bit, and I swear this pic pretty much sums up one of the key methods they were teaching.
Basically just tricks that a lot of people figure out to simplify problems.
That’s exactly what it is. A way to help conceptualize and play with numbers. Stuff my bored ass was doing in school anyway before common core came around lol
Common core is still a thing. I wish I had common core as a kid. Makes way more sense.
10 + 7 = 17 17- 1 = 16
9 is one less than 10, and 7 is three less than 10, so combined, they’re four less than 20 = 16
The legend said that it is how Gaussian elimination was discovered in europe
Why wouldn’t you take the 1 from the 7 so it is 10+6?
This is what I go for…Just play in 10s. Alot easier IMO
NOT LIKE THAT YOU HEATHEN
Idk I have adhd and my working memory is so poor that memorizing time tables was the only way. :/
I mean, sure, the choice of the “nice” numbers here is eccentric, but this is essentially the way math is taught nowadays. Only, instead of making 8 in this special case, the goal is usually to make 10 + leftovers because adding to 10 is always easy.
Here’s my (upper midwest) spicy mental math take: it should be big-endian and solved with backtracking for ripple carry/borrow. None of this starting-from-the-1’s-place-and-successively-incorporating-higher-order-digits nonsense. Extended carry/borrow is rare, and if you start with the most significant digits and give up/get bored part way through, the intermediate answer is in the ballpark of the real answer.
No take one from 7 and its 10+6=16
Take 7 from 7 and its 16+0 =16
Take 11 from 7 and it is 20-4=16
This is how I think for sure.
That’s the sort of thing “new math” was trying to teach. Those sorts of breakdowns are exactly what the kids who were good at math were always doing, and teaching methods eventually caught up and realized they should just teach the tricks.
Then a bunch of parents who were bad at math asked “new math? How can math change?” The fact that they even asked that question showed how their math education was lacking, but they seem to have won.
Exactly. Math has historically relied on rote memory for most mental math. Kids would have to fill out their times tables, addition tables, etc until they memorized them. I still remember getting pop quizzes in elementary school that looked like this:
You only had two minutes to fill out the entire thing, which meant you only had 1.2 seconds per answer. You didn’t have time to actually calculate them. The point was that you were expected to have them memorized ahead of time instead of calculating each one.But rote memory is laughably bad at actually teaching concepts. You may know that 12x5 is 60, but you don’t have any understanding on why, or other ways to do that same calculation without rote memory. And rote memory is only decently reliable up to ~12x12. Anything past that, and it becomes too much info to track; kids simply start forgetting answers.
The kids who were good at math (and I mean actually good at math, not just good at memorizing things) quickly devised methods to do this shit in our heads easily. Keeping track of multiple numbers in your head gets confusing. So “line them all up, add straight down, and carry 1’s” sort of falls apart if you’re doing it in your head. Especially if you’re trying to keep track of more than three or four numbers at a time.
Essentially, 127+248+30 is the same as 105+250+50, but the latter is much easier to parse in your head. But yeah, the parents (who primarily relied on rote memory) didn’t understand why the new method would be more effective, because they didn’t understand the concepts surrounding the math.
i used to hate the times table but i definitely think it’s essential to mental math. even if you vaguely remember it it will help. like knowing 42 shows up somewhere in the 7x and 6x may help you remember 6x7. or if you remember a neighbor you can just add or subtract the number once. for example if you don’t remember 7x6 it definitely helps to know each neighbor (both of which are easier to me since one is a 5x and one is a square number)… so either you think about 7x5 which is 35 so you can add another 7 to it or 6x6 which is 36 so you can add another 6 to it.
Oh I agree. My point wasn’t to say that rote memory is useless. I simply wanted to point out that it’s bad at teaching concepts. By teaching the concepts first, students are better prepared for later (more complicated) math courses. Anyone can memorize that 8x8 is 64, but understanding how to arrive at that answer is just as important.
I’m all for the multiple paths to solutions, but they aren’t even doing times tables these days. We drill it a little at home, but he struggled with just getting it memorized. I don’t know why they don’t drill a little. Honestly, they seem to have the kids sitting on the computer doing adaptive math most of the time.
yeah obviously, but i thought they were supposed to teach the times table after multiplication in general anyway
I think it’s good to have a good set of these tables memorized and then based off those you can bounce your tricks. Eg if you know 5x12 by heart, you get 5x24 by intuition. Or even if you know 24/2 for that matter. I use simple examples but this could scale to less memorable numbers too.
x5 has its own trick, for me it’s ÷2x10 (or x10÷2, whichever feels more intuitive) so 5x24 => 24/2 => 12x10 = 120
It’s really helpful for quadratic factoring, too, since knowing at a glance that –56 is ±7 × ±8 keeps your working memory free to actually focus on the mathematical skills/concepts/problem.
Strongly disagree that memorization isn’t important. It’s THE foundation to be able to do effectively do more advanced stuff.
Take the equation (5678 • 9876). Use long multiplication and you only rely on doing a bunch of single digit multiplications and additions. It’s so much faster to be able to instantly know each step instead of having to recalculate these “atomic” steps again and again in your head.
You generally don’t need to be able to solve multiplications involving double digits in your head. It’s nice-to-have but otherwise useless, as long as you’re able to calculate the ballpark of the result.
For example, (38•63) is roughly 2400 and I can then calculate it on paper instead of in my head.
Head calculations are just so much more error-prone than written calculations. Don’t do them if you can avoid them. There’s a reason why math students (at a university) are infamous for being unable to make the simplest calculations in their head. It takes effort that could be spent somewhere else.
I would argue that memorization is important, but what you memorize and how you arrive at that is very personal. Forcing kids to memorize very specific things, and trying to enforce memorization (as opposed to the ability to arrive at the solution) seems like a bad idea to me.
I still don’t have the 10x10 multiplication table memorized, and I took physics in high school and work as a programmer. I have a use for knowing number multiples, and have domain-specific numbers memorized (2^8=8*8=256, 256*256=65536), but what I don’t remember off the top of my head I can figure out from the things I do know, from certain tricks, and from brute force mental math juggling numbers.
And the important thing to me is, I learned what I know not because somebody told me this is how I should do things, but because I picked them up as needed, a mix of memorizing common multiplications and figuring out tricks (like multiples of 9*N for N<11 being the digits N-1 and 10-N)
I strongly disagree that memorization is important or foundational to advanced math. It definitely is useful, but you don’t need it. And the more advanced your math gets, the less valuable it becomes.
My experience is that university-level math explicitly tells you to not memorize values and formulas, but to get comfortable finding solutions directly, because then you actually learn what is going on and have methods that are universally useful.
In the real world memorization is even less useful. You will never be as fast and accurate as a calculator, or remember as many values as a precomputed table has. So why bother?
I meant basic memorization, not any advanced stuff. If you have to re-derive everything basic from scratch again and again, you will be less effective at advanced stuff.
This is not to say the basic stuff should just be memorized. Rather, it should first be understood and only then be memorized.
And definitions must be memorized, otherwise you’re screwed. For instance, try proving something is a group if you forgot the definition of a group. Yes, the definitions have reason for being the way they are (which you will likely learn) but definitions just cannot be derived from your mind during an exam.
In OP’s example with memorizing multiplication tables instead of doing them on-the-fly: This is a core skill required for so much later on. You don’t want to waste time and energy thinking about how e.g. 7•8 = 7•2•4 = 14•4 = 14•2•2 = 28•2 = 56 because that’s a quick way to lose focus. Especially if you – like me btw – have to invert a 7x7 matrix with two variables x,y put in a bunch of positions (and linear combinations of them) in an exam.
Edit: substitute unescaped *s with •
I only sort of agree. I still think that by forcing you to do that, by making you practice, makes the calculations “muscle memory” in that you aren’t memorizing the answers but can do the calculations faster and faster each time.
Sure. Some people could memorize them. But others will learn to calculate quickly.
It frees you up to do more complicated arithmetic. Geometry would be too slow if you didn’t innately understand
3*60=180. Which you don’t get without3*6=18
I was trying to explain how and why they were teaching math to a family friend and they didn’t get it(multiplication stuff). I broke it down with pen and paper and they didn’t get it. Simpler example, nope. Eventually I had to explain how multiplication is just repetitive addition. They responded with WHAT! and I realized why they always wore open toed shoes. I sent them a link for 5th graders.
Hey! Nothing wrong with open toed shoes damnit.
I’m not very good at math (but not an idiot like your example) and I wear flip-flops every day of the year but they’re not related.
Are you trying to say something like “too dumb to tie shoelaces?”
Because there are quite a lot of lace-up open toe shoes and sandals, as well as closed toe shoes without laces, so that doesn’t track.
Can you count to 20 with your shoes on?
I can count to 20 with my eyes shut but my toes can’t breathe with shoes on.
As a parent who is bad at math, you’re not wrong. But given my kids are excelling in math (very high scores), I’ve learned to shut the fuck up about it and let the teachers do their
black magicjobs.I want to add that when I said they give away that their arguments demonstrate why math education needed to change, I do mean it. This is a clear cut case of the education system failing them.
I’d normally be happy to throw snark at the idiot things parents say that make our education system worse, but not this time.
Those sorts of breakdowns are exactly what the kids who were good at math were always doing, and teaching methods eventually caught up and realized they should just teach the tricks.
Well… kinda. “Getting to 10” was what New Math was trying to teach. So you’d take the 1 from 7 and give to 9, because 6 + 10 is easier than trying to finagle your way to 8x2.
Then a bunch of parents who were bad at math asked “new math? How can math change?”
You don’t have to be bad at math, strictly speaking. But there was a lot of brute memorization in traditional math. Times Tables, for instance, were something you just memorized straight up without thinking too deeply. Getting 16 out of 7+9 was something you just had to do on your fingers until you had it lodged in your head.
Old Math tended to be slower and more tedious. New Math is more logical, but also somewhat counterintuitive until you get into the swing of it.
The fact that they even asked that question showed how their math education was lacking, but they seem to have won.
I’ve got friends with kids down in Houston. “New Math” appears to be alive and well, in no small part because it helps kids score higher on standardized tests.
deleted by creator
Never heard about new math. Where does this method comes from (geographically)?
The deep past https://en.m.wikipedia.org/wiki/New_Math
Thank you.
deep indeed
Always upvote Tom Lehrer!
not even ADHD related you’re just taking a route to something more readily available in your memory. that’s how brains are supposed to work.
to me the detour is -1+10. whenever i see a 9 i take 1 away from the other guy and then add 10.
9 x single digit mumber works similarly; except i take away 1 and complete that to 9 by adding a number next to it.
9x7 = ?
7-1 = 6
6+? = 9
9x7 = 63
9x7 = 70 - 7 = 63 in table of 9 too easy ! (nearly the same technic)
8x7 = 70 - 7x2 = 70 - 14 = 6 + 70 - 20 = 56 (6 from 10-4 from 14)7x6 = 5x7 + 7 = 70/2 +7 = 35 + 7 = 42 the answer to the life, the death and all the rest (5xa = 10/2 x a= 10a/2)
i mentioned the 5x trick elsewhere under this post but for me for some reason doing the halfing first is easier. so to me it’s a/2x10 instead.
Why wouldn’t you just take 1 from 7, add it to 9, and make it 10 + 6? That makes a lot more sense to my brain at least.
He’s a spider monkey with base 8 fingers.
Because making shit equal, be in perfect balance or even symmetric makes my dopamine go 🥳.
Finding the correct answer that way is a neat side effect too.
Multiplying by two is a similar cognitive exercise to adding 10 in small numbers (for me) so it would really depend on which occured to me first.
Because that is the joke and why the teacher reacted that way.
Or translated into reddit: woosh
Borrow 1 from the 7 leaving you 10 and 6. This is what they tried to teach in schools for awhile but adults weren’t getting it. Common Core? Is that what they called it?
As someone who learned not via Common Core, and then found out Common Core taught math how I taught myself to do mental math I was a little envious that kids would learn my “easier” method.
Same, common core is what I came up with to do mental math.
Yup, helping my kiddo with the math portion of Common Core was like seeing professionals finally understanding how easy it is to sort numbers to make stuff easier instead of doing a bunch of rote memorization of tables. Also teaching kids to estimate to know if your math is way off!
Common Core for math was awesome. That was the only one I had to help with so no idea about the rest.
Well it’s good for some shorthand but anything complicated you need either a calculator or do it long hand. With calculators everywhere they may have just switched to “hey fun mental ways to think about it because no one does long hand anyway”.
No, the same fundamental concepts works extremely well for multiplication of large numbers and long division, both of which don’t have a memorization option. It also helps with catching typos when using a calculator.
Easy long numbers yes, complicated long numbers I’m gonna say no. I’m not even saying large numbers, I’m saying long numbers which can include decimal points. And the chance of mistakes goes way up. There’s no point of doing it mentally or by hand when calculators are ubiquitous. I think this is why they switched to different ways of thinking about math, rather than hard core hand calculations that no one is going to do anyway.
Decimal points don’t make it more complicated when you understand the fundamentals.
Using a calculator is not a different way of thinking. You have to understand the math to know whether the calculator is being used correctly, the calculator just makes it faster.
One of my wifes friends was an elemetry school teacher when common core was popular. We asked her what it was and as she was explaining it, i said, “oh, like how you do mental math?”
Im an engineer and i just assumed thats how everyone did math… apparently people just memorized everything
Yeah, when I went through school they didn’t teach it this why but that is what I taught myself, much more simple math (+ & - with no * or \) in the same amount of steps.
Is that what they call Common Core? I’ve heard the term but didn’t know how it changed the method of teaching math.
Leave it to my AuDHD brain to figure out a less strenuous path to the same endpoint…
I wonder if this is an anxiety source for ASD/ADHD/AuDHD people. Having to constantly re-map lessons taught to fit my neurodivergent brain that it now feels like the entire neurotypical world is gaslighting neurodivergents.
Just a heads up, your \ got absorbed by the text markdown Lemmy uses. You have to use a double slash to have it show up, like this
\\.Fixed, thanks again!
Oh, thanks so much for the heads up. I didn’t know that!
Sure thing! It’s not a particularly well-known thing, tbh, so it slips into comments now and again.
Is that what they call Common Core? I’ve heard the term but didn’t know how it changed the method of teaching math.
Common core showed multiple ways that were intended to increase the understanding of how math works. This was one of the ways that was presented which wasn’t how they taught it when I was a kid. There were at least two that I remember when my kiddo was doing common core:
- Double one of the numbers and add or subtract the difference between them (7 is two less than 9, so 9x9 then subtract 2)
- Take enough from the smaller number to reach 10 and add what is left (9+7 to 10+6)
The answer is 69
420% of the time.Niiiiice
And here I always thought it was 1001 + 0111 = 10000.
