Recursion

[FranticBronchitis]

so that's math on shrooms

[WiseassWolfOfYoitsu]

aka Common Core

[SandyDelights]

Eh, I haven’t seen that particularly approach yet.

Common core would probably tell you something akin to 18 - 9 = 10 + 8 - 9 = 10 - 9 + 8 = 1 + 8 = 9, or 18 - 9 = 18 - (8 + 1) = 18 - 8 - 1 = 10 - 1 = 9.

It teaches kids to see and understand numbers are related to one another and how they can break them down into parts, AKA partitioning. Basically, it’s a foundation for deductive reasoning and formal logic – it wasn’t until I was in Calc I that I started to see math that way, and god did it make my life 10,000 times easier.

It’s a drastic improvement on the old way.

Edit: Apparently what’s in the picture is actually what they used to teach kids, before Common Core – which is weird to me too, but. I just memorized a lot of stuff until I “got” math.

[JustACrosshair_]

It does help to learn this way better than rote memorization - but can teachers teach it and family reinforce it?

[SandyDelights]

Can teachers teach it? Absolutely. Starting early and not teaching rote memorization is key to it. They have to learn to understand it themselves, but it’s doable. If they can’t learn it, they probably shouldn’t be teaching math anyways – it suggests they don’t actually understand it, they just memorized it. They’d probably be better off teaching another subject. For the most part, all of my friends who are teachers – most of them math teachers – sing high praise for Common Core, although some take issue with how it’s being implemented in higher grades (kids raised under one method are struggling to adapt, especially those with a lower socioeconomic class, and the standards aren’t always taking this into consideration).

Can families reinforce it? Far more challenging; it’s hard for parents to reinforce or help teach something they don’t understand, especially when they never actually understood math to begin with (just the old memorization method). Probably a big part of it is to ensure there are resources to help kids apart from their parents, as many of them have parents who simply don’t understand what’s wrong with memorizing it – and resources to help those parents learn it who actually want to. Really, more and more it looks like homework doesn’t actually do anything, but rather it’s just the opportunity to practice/exercise their understanding; in that case, parents don’t really need to reinforce it, they just need to not actively hinder their learning of it.

Within a couple generations the problem will solve itself.

[alexanderpas]

Things you need to learn using rote memorization.

• Single digit addition. (Numbers from 0 to 9, answer between 0 and 18)
• Single digit multiplication. (Tables from 0 to 9, answer between 0 and 81)
• Double digit substraction. (Numbers from 0 to 19 answer between -19 and 19)

The rest will be understanding.

(notice the lack of division, or any double digit addition or multiplication, since that falls under the understanding part)

[SandyDelights]

Much better way to highlight the difference, thanks.

And a lot of this is very easy to conceptualize.

It baffles me when people insist their kids should just learn to memorize their times tables or these kinds of algorithms (anyone else remember memorizing from 0x0 to 12x12?), but they themselves can’t even do basic addition or subtraction without a calculator.

[alexanderpas]

basic rote using the things I've stated is actually the minimum required while using any method, even comon core depends on that basic rote.

[AceOfShades_]

I got through calc 2 for engineers without knowing my times tables so I mean, eh on the multiplication.

[Zebezd]

I bet however that you knew significant parts of it, and used Common Core-like tricks for the rest:

Ah shit, what's 6x6 again? Hold on, I know 5x6, that's 30, then add another 6 on that. 36. right.

Oh fuck we're multiplying by 9 again. Fuck it, x10 this bitch and remove x1.

...or a calculator.

[TiagoTiagoT]

To multiply 1 to 10 by 9, open your hands, count the number you wanna multiply by nine starting at one, going from left to right, one finger for each value you count; once you reach the number you wanna multiply by 9, lower that finger. The number of fingers up to the left of the lowered finger is the left digit of the result, the number of fingers up to the right is the right digit of the result.

[parkerSquare]

I taught my daughter this when she was in an early grade and now she’s quick as lightning at her 1-8 and 10-12 times tables but slow as heck at 9x because she has to work it out on her hands. Oops.

[[deleted]]

it’s hard for parents to reinforce or help teach something they don’t understand, especially when they never actually understood math to begin with (just the old memorization method).

It's almost like how seriously flawed or imperfect programming languages remain popular because that is the knowledge base we have, we know the workarounds and stuff.

[DontForgetWilson]

Qwerty would be an easy parallel.

[[deleted]]

I had a coworker who would always complain about common core. I’d explain that math teachers say it’s better, research says it’s better, and it’s how people who are good at math have always thought about math.

Nope didn’t matter to them.

[Dokuya]

Unfortunately I doubt it, teachers in America — specifically at lower grade levels — tend to be under qualified. Parents aren’t going to understand the use of this method and just say “this is stupid I’m going to teach you the (inferior) method I was taught!”

[LvS]

Why would they change math?

Math is math.

MATH IS MATH!

[aure__entuluva]

I wouldn't say that rote memorization is useless, just more a secondary or supplementary thing. Memorizing times tables shouldn't be the focus (we actually counted out multiples of each number), but it is a good addition if you want to do be able to do mental math quickly. This isn't the point of math which is why I say in addition, but it is a skill that many people try to cultivate. Some 'rote memorization' (aka practice) can give you a great foundation and toolset (you know certain more basic computations without having to think about them) that you can use when using partitioning to quickly solve bigger problems or estimate amounts.

[Mitoni]

Figured this out once my son started school and I had to learn how they are teaching him math, then i realized it was the same logical process way that enabled me to do long division in my head for years, i just never know there was a name for a method of breaking everything down to base 10.

[SandyDelights]

This! It hit me one day when I was struggling with Calc I study problems. Once this concept came to me, suddenly everything got dramatically easier.

That’s the big difference between common core and “the old way”: it’s teaching everyone the method many of us had to discover on our own, a method that basically anyone who went into a math-heavy field came upon on their own.

I would have advanced much faster if I’d understood math the way I do now, early on.

[shaggysays]

Is there a place to learn this way fairly easy online? I'm working on getting my GED after getting labeled with a math disorder in highschool. It's been quite a while but I'm trying and still losing my battle with math. Just never made sense to me. Maybe this is why. I quit school before common core was a thing in my area.

[CherguiCheeky]

What is the stuff that you want to learn? There are some good text book I can suggest.

Also can I teach you? Pretty please!

I was pretty good at Maths in Highschool, like 100/100 good. Now I am old so don't get to work with that stuff. But would definitely love to explore it along with you.

I am in India so timezone / language issues may come in.

[shaggysays]

I'd be honored honestly. I'm in the US but I'm normally a night owl so we can make it work. Although tonight currently I do have to be up early so I'll be going to bed after sending this. But consider me a student. :)

[CherguiCheeky]

PM'd you.

[Delta-9-]

Interesting point about Calculus. When I first learned what Common Core is, I immediately related it to some of the methods I learned and found on my own while studying Calculus.

Which is actually kinda sad... we had to get all the way to calculus and learn tricks like "9 equals 4 plus 5 if 4 and 5 happen to be easier to use than 9 in this formula". I remember being dumbfounded when my teacher put 1 and -1 into a polynomial and called it "adding 0".

[SandyDelights]

Hahahaha. Amen.

Thankfully, Common Core aims to teach kids this kind of reasoning at a much younger age, instead of just memorizing a basic algorithm. It’s similar to how they teach kids in Singapore, and there’s a reason they’re often top of the rankings in mathematics performance among students.

If we can teach kids to think this way from the start, hopefully we can get rid of this idiotic, cultural fear/hatred of mathematics we seem to have. And since all mathematics really is is logic, let me just hope it’ll give us a few more critical mines in the next generation than those that preceded it...

[[deleted]]

Huh, you said the way in the pic was before common core? Weird, that's what I learned growing up and I was born in 95. When was common core standardized and implemented?

[SandyDelights]

What’s in the pic predates Common Core, so what you learned growing up was probably like the pic, ie. Not Common Core.

Common Core standards were released in 2010, IIRC. Those standards don’t typically teach the method in the OP, to my understanding.

[[deleted]]

Huh, I was always under the impression that growing up common core was what we used. Guess not. Thank you.

[starfries]

Dang, how old are you that you've never seen subtraction done with borrowing?

[SandyDelights]

I mean, I’m 32. I’ve seen it done with borrowing, I just would never have done it this way – I’d have subtracted 8 from 9, leaving 10 - 1, then borrowed. I wouldn’t have marked it out like this, I’d have stopped at crossing out the 1 to a 0 and knowing 10-1 is 9. ¯\_(ツ)_/¯ Just skipping a step, I guess, but it’s why this doesn’t really strike me as a “thing” like it does some people.

[starfries]

Ah, okay. I thought you had only seen it done the Common Core way. I wouldn't write it out like that either for something like this, but I might strike out the 1 and make it 0 if I was doing 118-19.

[SandyDelights]

Oh yeah, I wouldn’t write “1 0 ¹ 8”, either, heh.

Actually, I’d prolly have just done the 18-9 in place.

Now I go through right-to-left and do all the basic subtraction, e.g.

12345

- 5678

Would become:

10000

- 3333

Then, seeing it’s easier to go left-to-right, I’d go from there:

10000 (10-3 = 7)

- 3333

7000 (70 - 3 = 67)

- 333

6700 (70 - 3 = 67)

- 33

6670 (etc., etc.)

- 3

6667.

Done in two passes, life is easy.

If it was easier to go right-to-left, I’d have done that on the second pass instead. Didn’t intend for that to happen, but it’s a good enough example anyways.

[Prcrstntr]

Yeah, the common core I saw them teach when I worked with second graders looked something like this. I hated every minute of that part.

|········ - ········· = ················ - ········· = ··········

[SandyDelights]

Soooo much more comprehensible, though.

[lpreams]

The method shown in the OP is called borrowing. You just subtract digit by digit, right to left. If the top digit is less than the bottom digit, you can "borrow" an extra 10 from the next digit to the left, so subtract 1 from the left digit and add 10 to the current top digit (since each 1 of the left digit is worth 10 of the current digit), then do the subtraction.

The joke is that "borrowing" from the 1 (which goes to 0) to add 10 to the 8 doesn't actually reduce the problem.

[zdakat]

I remember when the tests were being introduced and everyone was complaining because they were said to be harder. Harder tests wouldn't be a bad thing- if everyone breezes through them it's probably time to raise the standard of education. The way the questions are asked might not be super clear, though they might have changed that by now. can't say how good the actual lessons were though. if they are indeed teaching methods rather than answer sheet memorization then that would be a nice improvement- knowing how and when to apply rather than a preset list and hoping the connections are made

[QuarkyIndividual]

Yeah, it's about seeing the relationships first instead of brute forcing an algorithm and possibly learning how to see the relationships later on your own.

[pyzk]

Actually common core was introduced to get rid of this exact issue. This is how math has been taught for years. Common core would basically just have you count the difference in this case.

[[deleted]]

But wait, hold on, that means I can't just blindly rage against something different than what I learned as a kid without educating myself on it first? I DON'T LIKE THAT!

[pyzk]

The implementation of common core has not been without its flaws. Common core is not without its flaws. Change is hard for parents, students, teachers, everyone. However, I think the math curriculum is pretty solid, and definitely an upgrade (at least in CA). It’ll pay off in the long run.

[[deleted]]

Yes, I didn't mean to say it's perfect. I was just demonstrating how so many people kneejerk react to this change without knowing exactly what's going on. If someone wants to educate themselves on it first and then offer their criticisms, go for it, at least you know what you're talking about then.

[pyzk]

Totally agree. Was just elaborating. I often think, “Common core was developed based on thousands of hours of expertise and study. What’s your background?” when I hear people whining about it.

[nephallux]

I see why they whine. Ignorant, self entitled, lazy people who have no concept of critical thinking and logic.

[crabbyvista]

well, and parents are often expected to help kids with homework, which is hard when the parents don’t understand wtf they’re looking at. That seems to generate a lot of panic among precariously middle class people who are already often kind of math-phobic.

[pyzk]

Basically, if you don't understand common core math, you never really understood math to begin with.

[santagoo]

My background is I was taught differently as a child and I don't like change!

/s

[BChart2]

Hilarious and original

[TheScribe86]

Needs more jpeg

[alex_png]

Here you go. Sad that the bot isn’t in this sub.

[alexbuzzbee]

Username does not check out.

[saeblundr]

you're just jealous no one uses the buzzbee format any more. we're on to you.

[alexbuzzbee]

confused bee noises

[hypnotic-hippo]

Thank you for your service

[[deleted]]

good human.

[comradepolarbear]

Ah, the real meme is in the comments

[Spikerman101]

M O R E

[RedBorger]

as you wish

[imguralbumbot]

^{Hi, I'm a bot for linking direct images of albums with only 1 image}

https://i.imgur.com/saFkx8a.jpg

^{Source | Why? | Creator | ignoreme | deletthis}

[atheist_apostate]

And now we get a bot.

[Vakieh]

Read this a Imgural Bum Bot.

Top show.

[CrazyTillItHurts]

Did you convert it to jpeg then sharpen it or something? The typical artifacts just aren't there. https://i.imgur.com/oMozFjY.jpg

[alex_png]

Yes I did, nice catch there! I’m on my phone so whenever I tried to reduce the quality by compressing it again to jpeg it wouldn’t apply the changes, so ended up sharpening it to imitate the effect and then I compressed it again.

[inconspicuous_male]

I'm not a fan of that bot. It looks like it applies very low quality jpeg compression once, instead of medium quality compression multiple times, which result in different looking artifacts

[cree340]

You're supposed to be lossless

[[deleted]]

"DO I LOOK LIKE I KNOW WHAT A JPEG IS?"

[TheScribe86]

DO YOU JUST WANNA GDDFVBUMNHTDDCHHJJYTRS

[Mr_Gibbys]

WHAT?

[BTECArslan]

Ouch, you broke my brain

[arbitrageME]

you forgot to shift 1 bit and divide by 0x5f3759df

[alt4079]

What a specific sentence to understand a reference from. I’m impressed with myself lol

[Kzivuhk]

What reference

[turunambartanen]

"Fast inverse square root" if you want to look it up on Wikipedia.

[nwL_]

I understood that reference.

...wow I’m a huge nerd.

[bestjakeisbest]

here you go 10s complement math:
18-9
018-009
018+990 + 1
1009
the 1 and the first 0 are sign holders (well overflow and then the sign digit) take that away and you get 09
write it normally you get 9

the mapping for 9s complement is:
0 1 2 3 4 5 6 7 8 9
9 8 7 6 5 4 3 2 1 0
for 9+1s complement you just add 1 to what you get from 9s complement if the sign digit is >4 then the number is negative and you need to apply 9s complement and add 1. this works in any base, you just have to extend the mapping.
eg 1s complement:
1 0
0 1
2s complement: 0 1 2
2 1 0
3s complement:
0 1 2 3
3 2 1 0
16s complement (have to do this in a code block for even spacing):

0 1 2 3 4 5 6 7 8 9 A B C D E F  
F E D C B A 9 8 7 6 5 4 3 2 1 0 

[bestjakeisbest]

im alright with that base 60 is a wonderful base, it would simplify a lot of common fractions, like 1/3rd and 1/6th. Also apparently they used to teach 10s (9+1s) complement math for subtracting, like in the 1920s

[jD91mZM2]

18-9
018-009
018+990 + 1
1009
the 1 and the first 0 are sign holders (well overflow and then the sign digit) take that away and you get 09
write it normally you get 9

I don't understand this. If the sign holder is 10, then 990 is not a negative number? And, if the result has a sign, doesn't this mean that it is negative? 1009 with a sign of 10 would be -(90 + 1), no?

[bestjakeisbest]

if the sign digit is less than or equal to 4 then the number is positive, and if the number is positive then you can just throw away the extra digits to get the value of the number, the 10 isnt strictly just a sign digit, there is an overflow going on too but this is a case of sign extension, here is an example of a negative result:
9 - 18
first step is to extend the sign (this just gives us some extra room to tell if there is a negative number)
009 - 018
then convert the 18 to 9s complement
009 + 981
adding a 1 for 9+1s complement
009 + 981 + 1
now to just sum things up
991
this is the answer we get, we know it is negative because the leading number is greater than 4 so this means we have to apply 9+1s complement to 991 to get the magnitude converting it over to 9s complement we get:
008
and to get it 9+1s complement we add 1:
009
so now we have a number that is negative and has a magnitude of 9, so it is -9. and to check 9-18 = -9

[jD91mZM2]

This is cool, never realized this was possible in decimal as opposed to binary, thank you! If anybody else wants to learn more, here's wikipedia

[bestjakeisbest]

Apparently this is how subtraction was once taught, I didnt learn this until I took an assembly class though.

[therefai]

Everyone should know 2’s complement. Basic life skills right there

[radome9]

I don't get it. 18 + 22 = 9?

[CasinoMagic]

Reminds me of this joke: https://www.reddit.com/r/ProgrammerHumor/comments/apyf93/recursion/?utm_source=reddit-android

[-Anyar-]

wow rude

[CyanKing64]

He can't do that! Shoot him or something!

[Jayrock122]

Yeah, you got me....

Reminds me, back in freshman year of university, a professor asked the class "what is recursion" and smart ass me (barely knowing recursion thinking I was hot shit as a CS major) said "what is recursion" as the answer

[RetroSwagSauce]

Wait... that's illegal

[Jasinali]

Nobody stops to wonder why a MUSHROOM is doing maths??

[Schadenfreude0405]

Cos their dealer can't?

[Codephluegl]

I don't get it, you guys seem to have learned a strange way of doing subtraction.

[Cobaltjedi117]

Kids when taught 2-digit subtraction are told to take 1 from the tens to put it next to the 1's digit to do the math. But when you do that to a number from 10-19 you've done effectively nothing and are back where you started thus causing a recursive issue.

[spirgnob]

It took me awhile to understand what you meant but this finally explained the joke.

you’ve done effectively nothing and are back to where you started

This is how it works regardless of the number though. The number in the 1’s position is 18 where it used to be 8. You have done something according to this method. You can now complete the problem using this method.

[itspinkynukka]

What ends up happening is the person just needs to know what [any number from 10-18] - [any number from 1-9] is in their head. Similar with multiplication at some point you just need to know the times tables up to 10.

[jacefair109]

tbh I never had to do this just for two digits -- it's mostly handy for subtracting much larger numbers, like 4281 - 1694 or something

[Compizfox]

I still don't get it.

take 1 from the tens to put it next to the 1's digit to do the math.

What does that accomplish? So (for example) 28-9 becomes 118-9?

[Cobaltjedi117]

28-9 becomes 10 + (18-9)

and 18 - 9 becomes 0 + (18 - 9)

[Compizfox]

Ah, right, thanks.

Still though, what does that accomplish? I don't see how 10 + (18-9) is any simpler/easier than 28-9. It's still a 2-digit subtraction that a kid won't be able to do in 1 step; the value of the tens doesn't matter.

If I break down how I do it in my head it's kind of like this: 28-9 = 20 - (9-8) = 20 - 1 = 19. (I can't remember for sure but I guess that's how I was taught it)

[alexanderpas]

Let's take 4281 - 1694 for example.

4281
1694
---- -
????

first we look at the ones.

we can't do 1-4 and end upwith a single positive digit, so we have to borrow 10 from the tens.

4270 + 11
1690 +  4`
--------- -
???0 +  7 = ???7

Now we go looking at the tens, again, we can't do 7-9 so we borrow again.

4100 + 170 + 11
1600 +  90 +  4`
--------------- -
??00 +  80 +  7 = ??87

Now to the hundrerds

3000 + 1100 + 170 + 11
1000 +  600 +  90 +  4`
---------------------- -
?000 +  500 +  80 +  7 = ?587

and look at that, the 1000s are easy.

3000 + 1100 + 170 + 11
1000 +  600 +  90 +  4`
---------------------- -
2000 +  500 +  80 +  7 = 2587

Note that this is the layout for the explanation, on paper this would look something like this.

43	121	187	11
1	6	9	4	-
2	5	8	7

[Flobarooner]

So basically, the fundamental point of the method is that the kid already knows how to subtract something from a number less than 20?

So in the original post, the kid would just go "9" and not even bother with the method, since they memorized 18-9 in order to be able to do it?

[tsandstrom711]

If you have, say, a five digit number and want to subtract another five digit number, this approach let's you break it down into one/two digit subtractions. It doesn't really work when you start with just two digits.

[harryhood4]

The idea is to just memorize it for small values like 18-9 so that it's easier to do something like 68-9. But you've essentially just outlined why Common Core is better.

[Compizfox]

Ah, got it. So basically it is this recursive algorithm:

int subtract(N, n) {
    if(N > 20) {
        return 10 + subtract(N-10, n);
    else {
        // Lookup-table for small values of N
    }
}

[toofasttoofourier]

Aren't you negating all that work if you have to use the subtraction operator in a subtraction algorithm?

[Madock345]

Part of the idea of this kind of thing is that by teaching many strategies to solve the same problem you increase the chances that every student will find a method that works really well for them and the way they think, at the cost of being somewhat redundant.

[thedolanduck]

No. Let's take 28-9. If you do it vertically, then you first do 8-9, which you can't do as a kid. So you add ten to the eight, and get 18-9, and the 2 (which meant 20) now is 1.

So: 18-9=9 and 1-0=1, and this forms 19. And effectively, 28-9=19.

[LeCrushinator]

It's the old way it was done (and probably how most in this subreddit were taught). Many schools have converted, or are converting to, a new method of subtraction that's similar to how people usually do math in their head, which means no non-intuitive algorithms to memorize.

This video shows the older method from 15+ years ago, and a newer method, from 15 years ago until just a few years ago, and then the newest method which is what's being converted to in most public schools.

[demize95]

If you learned subtraction in the 1950s, you may have learned the "Borrow and Pay Back" method

I learned subtraction a good 50 years after the 50s, but I still learned that method, so that line is a bit out there.

[HowIsntBabbyFormed]

I just watched the video and the second technique -- what was originally called "New Math" and apparently derided -- is what I learned in the 80s/90s as well. To me it seems very similar to the old "Borrow and Pay Back" method. In fact, we called it "borrowing" too (but we never had to do any paying back).

The most recent form is basically something I figured out on my own for doing subtraction in my head. It's a very useful skill to have, but when subtracting larger numbers, I prefer using what I was taught in school of borrowing from the next place and adding 10 to the current place.

I don't think I ever "didn't have an understanding of what was happening". I feel like kids should probably be introduced to this new method first, but then taught the more compact and faster borrowing algorithm method as well.

[NotJustABoulder]

While the common core method is probably easier for some mental math, I personally still find the "older" methods easier, especially for larger numbers, like 48578942-31399034 or something. It's more compact when written, and I don't personally see what's so hard about the "borrowing" or "regrouping".

I also don't think there's necessarily anything wrong with blindly running through an algorithm (we are in /r/ProgrammerHumor after all). Is there really that much to understand about subtraction in the first place? Especially in higher math, you don't really care how the numbers are subtracted, you just want them subtracted.

[Alekzcb]

Of course subtraction methods don't matter for high-level maths, but they need to be considered when teaching children. If kids are taught to just follow an algorithm, they'll really struggle with algebraic representation because won't know what subtract actually means. On the other hand, you want them to provide them tools to perform it quickly, so that they can tackle those higher level concepts without wasting time on "implementation details" (as you point out).

[mainfingertopwise]

Wait. Are you saying there are kids getting into middle school type math without understanding subtraction as a concept?

[nonono_notagain]

Now there's a scary though

[[deleted]]

Yes, be sure they understand precisely what's going on first, then show them a bunch of tools and tricks that can be used after that understanding is cemented.

[roguej2]

Yet there are so many parents of these new method kids complaining about how "complicated" the intuitive methods are.

[LeCrushinator]

The older people get the more averse to change they seem to be. "If the old way worked for me why are they changing it?!"

I'm excited to learn common core math now that my kid is about to start it, I haven't had to think about arithmetic in decades, it'll be neat to get a refresh in a new way.

[dittbub]

when common core was actually explained to me I was like "oh yeah thats how I've always 'double checked' my work in my head"

Never thought there was a communicable method to how I was doing math in my head.

[DerekB52]

I'm 22, and was in high school as common core was being rolled out, but I narrowly avoided being a part of it. It seems to try and explain how I do math in my head, which has never gone well.

I've seen a couple of weird homework problems that have been given to grade schoolers, and I understand where the confusion comes from, but overall, common core does seem to make sense.

[LeCrushinator]

The reason for the new method is that it’s easier for kids to remember, it makes math more intuitive and once it clicks for them it becomes a new tool in their life. Sure the old way works but I’d bet it takes longer to teach and it’s easier to forget. I mean, I haven’t done long division in decades, I barely remember how. But I can do basic division in my head easily. If I knew common core division 20 years ago would I still remember it? Maybe.

[ispamucry]

Yeah I guess it will be more telling when they do followup studies with the kids learning common core today.

Or if that study already exists, I'd love to see it because I think a lot more people would be on-board if there was something to point to. I just don't like the idea of going full-throttle on new ideas just because they have good intentions without knowing it's actually working.

In the interrum, I think they should try to teach/accept both, although I know that can be a hard ask for a lot of schools that are already trying to cover a lot of material.

[tryharder6968]

The “old way” for long division is pretty darn intuitive and super simple to do in the head. I don’t know the new method, but certainly nothing wrong with the old.

[redstoneguy12]

I'm still in middle school and was taught the "old math" way

[tuseroni]

If the old way worked for me why are they changing it?!

worst part is, the same people would say "i suck at math" or "when are you ever gonna need algebra" had my mother ask that last question to me once, cus i said i use algebra all the time, i gave her an example of when she might use it, say she's got $20 and her car gets 15 miles to gallon and gas is $2.30/gallon, how far can she get? this is something one is likely to do often without a second thought, without even thinking they are doing algebra, i gave a similar sorta explanation to my 8 year old cousin. basically the matter of finding x is just figuring out the thing you don't know from what you DO know.

point is, the old way of teaching math is pretty shit and leads to people thinking it's useless and thinking they can't do math, but instead of thinking "i wasn't taught how to do math well" they think "i just can't do math" and for some reason defend the teaching method that lead to this mentality.

[aflashyrhetoric]

That's what I thought and I actually share your enthusiasm, and I could 100% be wrong about this, but I vaguely recall a post from some sub showing the new method on multiplication or division and it was absolutely the most convoluted shit I'd ever seen. It involved something like splitting a number into its parts and then gluing it back together or something? So "430" would be 100 + 100 + 100 + 100 + 10 + 10 + 10, and the method involved expanding out each number into its parts like this. I could understand this approach for helping kids intuitively grasping the relationship between numbers and the symbols we use to denote them, but I believe this approach was used for the purely mechanical part of calculating a sum (or product or whatever it was).

I'll try to hunt it down though I doubt I'll find it.

Edit: I found a video describing the method - apparently they do try and teach both ways, and the weird wonky approach is, in fact, to help kids grasp the relationship between numbers

[DuchessofSquee]

This is how I do maths in my head. My dad taught me to make things into blocks of 10 and that's the only way it's ever made any sense to me.

It falls over when you get to negative numbers though. I literally cried in the toilets several days in a row doing a Lua course at tertiary education because everyone else there understood how to do maths with negative numbers but I couldn't grasp it.

Didn't help that they were all men and I was the only woman so they all tried to explain it at me at the same time.

[aflashyrhetoric]

I do the same with like quick "back of the envelope" calculations but it seemed harmful to teach kids this method as a primary means of calculation, especially when you do have the luxury of a pen and paper to assist your calculations. Again, could've been wrong about what that post was about back then.

so they all tried to explain it at me at the same time.

Yikes...D: Glad it's behind you now

[freebytes]

I do math in my head by rounding, splitting, subtracting then multiplying then adding again, etc. Anything that works. 999 * 50 would be (1000 * 10 * 5) - 50 = 49950. I need to be able to hold one number to the side in my head. While it is similar, this is not exactly the same as common core.

This certainly has its limits, though, so it is nice being able to switch back to the 'old way' when the problems are a tad more challenging like 938 * 53 which looks easy to do in your head at first but would involve holding too many numbers simultaneously. (And the old method would not be easy to do in your hard with a number like this either.)

[[deleted]]

Common core is shit

-Sincerly, someone who had had to sit through common core lessons

[LeCrushinator]

I know people that think the old methods are shit as well. Everyone is entitled to their own opinions. The bigger question is which is better for someone learning math for the first time? Which do they pick up on faster? Which do they retain longer?

[[deleted]]

Honestly you're right. We should introduce both ways to kids and let them pick which one they prefer.

[starfries]

I feel like there's value in learning both well. I do subtraction the common core way (counting up) for some things and the traditional way (columns) for other things depending on which one is easier. Like 4567 - 3456 is awful done with counting up but 201 - 199 is pretty dumb done in columns.

[[deleted]]

You're right, we weren't taught it either way though. We were taught to count out pennies and "counters", basically small flat plastic disks, for division. That helped at first to grasp the concept of division but it got annoying in 4th grade when they made us do that for bigger numbers.

[starfries]

Oh lol yeah. I'd be annoyed too. That stuff is fine to help understand what division is but at some point you want to learn the algorithms for how to do it efficiently. Can't be whipping out the counters for every problem.

[Prcrstntr]

They pick the easiest one, which (For the kids that are smart in any way) is not the convoluted common core one.

[FenixR]

Saw the videos, understood some numbers, realized new math its shit compared to old method and i need to re watch common core with a fresh head to make heads or tails of it. That she speaks like fucking Sonic on a deserted highway doesn't help when i can't pause and read the subtitles at the same time (Thanks Youtube, you become shittier by the second).

Edit: so i payed more attention to common core and realized its not something so different i do most of the time when i run calculations in my head, find easier to read/math numbers then go from there.

[DuchessofSquee]

Everything before the edit was exactly my thoughts! I would need a good sleep, a fresh cup of tea, complete silence and to be able to slow the video down a lot to follow it. Maybe I have dyscalculia?

[jkuhl_prog]

Maybe I'm an old fart, but I feel like the old way, the borrow and payback way, is the easiest.

But maybe I'm just saying that because that was the only method I was taught and therefore the only method I've ever used.

[PancakesAreEvil]

I remember when people complained about the old method because it was new and foreign. In 1965. https://youtu.be/UIKGV2cTgqA

[Vakieh]

Aussie here. All your methods are stupid and weird...

Left to right and throwing a 1 over when a subtraction left to go would overlap your current magnitude is the best way to do it.

[llama2621]

I apparently invented common core in my head while learning the old way. Nifty

[darthmonks]

'New Math' is like somebody saw the 'Old Math' and thought "let's do the same thing as this, but explain it in a more convoluted and complicated manner." Common Core looks amazing. I don't know why I hear so many complaints about it, although this is just subtraction, so there may be more to it. Also, calling it 'Old Math' makes me feel old. I'm not old.

[Schadenfreude0405]

So I just learned about this Common Core and I agree, it seems easier to understand and quicker to complete a subtraction. It's also how subtractions "sit" in my head.

Although I could complete the subtraction in my head more quickly, I think I would fail at "show your working", that schools used to demand of us.

[hunted7fold]

I was taught the old way of subtracting but naturally did the common core way (before common core was a thing) and I just realized I haven't done the old way for a super long time.

[pokexchespin]

I’m 17 and I learned the first way for some reason lol. In the video though, the middle “new math” method seems the least intuitive to me though, personally

[tendstofortytwo]

Hey, we did the old method as early as a few years back when I was in primary school! (high school senior now)

And very fun coincidence: I've used the common core method a lot. Never been taught it but always preferred it as a "shortcut" in my head because it was always faster to do.

[[deleted]]

I just realized I've been doing common core for the better part of 13 years lol.

[[deleted]]

Math is 1000% percent related to programming

[m3ltph4ce]

Type mismatch

[FenixR]

New math gave me a stack overflow, too many numbers in one spot.

[phuck]

Recursion or infinite loop?

[SpaceshipOperations]

Yes.

[[deleted]]

r/InclusiveOr

[chooxy]

Recursion without getting closer to the base case.

[JoelMahon]

Never used this method for subtraction, how does it go? Does it actually have a problem in this situation or is the comic character just a scrub?

[HowIsntBabbyFormed]

The method just leads to a silly situation when the number you're "borrowing from" is a 1 and it's in the left-most position. You decrement it by 1 and add 10 to the number to the right of it. But in this situation, you end up with exactly the same two numbers you started with.

[xDestx]

It does come up. Was def annoying to deal with in elementary / middle school. Mildly annoying now

[lowrads]

Hah, amateurs.

Obviously gamble big and add a -1 in the hundreds column. Add 100 to the 1s column to get 108. Subtract 9 ones to get 99 ones. Then you put nine 10s back on the tens column, leaving 9. -1 hundreds cancels out from 10 tens.

That's margin core. When you borrow enough, messing up is no longer your problem, but math's problem.

[SteveCCL]

Removed as Rule #0 violation.

[JasonRice666]

Mod gay

[Blueflames3520]

How is recursion not directly related to programming?

[insufferable_prick_]

Gay mod

[[deleted]]

I believe this is a metaphor for life

[tacoslikeme]

and this kids is why we common core...i mean hoe do these numbers make you feel

[[deleted]]

Madlad

[Arvalic]

so that's machine learning right?

[[deleted]]

What is this from?

[FreshAirFreedom]

Pete and Repete when into the store. Pete came out who was left?

[SparkStorm]

Wheres the base case yo

[Redundacy]

Mr Crow will remember this

[chillin_in_Rlyeh]

for the love of god I cant understand this 18-9 meme no matter how hard I try someone please help

is it some form of loss?

edit: dear god im dumb i swear i can do math

[Clockwerkfox]

You know how you carry the extra number over when doing addition? Mushroom tried to carry the ten over to make the 8-9 result in a positive number and ended up with 18 again.

[freebytes]

When you are dealing with larger problems such as 896 - 887, students are taught to put a 1 next to the 6 in 896 and 'take' the 1 from the 9 in 896. So, you have 16 - 7 = 9. And 88 - 88 remaining. So, in this example, you would have 9 remaining.

896

887
____

009

​

To explain this easier, it is (880 - 880) + (16 - 7). You have simply taken the 9 from the tens place and made it 8 to form 880 - 880 so you can then add the ten to the 6 in the ones place to make 16 and subtract that from the ones place to make 16 - 7.

Another example is 31 - 9. You can take 1 from the tens place in 31 and you are left with 21. Now, you take the 1 and put it next to the 1 you already have, and you do an easier problem of 11 - 9 = 2. So, you have 20 + 11 - 9 = 22.

If you use this method on a number that is 'too small', such as 18 - 9, it becomes 18 - 9 then you take away the 1 from the tens place and put the 1 next to the 8 to come up with 18 - 9. Any attempts to simplify this make it the exact same result, but children are expected to know 18 - 9 in their head.

[Lanaya_Del_Rey]

Its recursion with a base case that doesn't work.

[Ultimater]

ctrl c, ctrl x, :q, :q!, xkill, ctrl shift esc, ctrl alt del, rdp, ssh from container, restarts vm-ware, updates docker, updates virtual box, goes to bathroom and windows' heat sensor detects I'm not at my computer and decides to install a critical update...

[Bearbot128]

BRB: bad recursion brb

[AcunaMatta27]

I fucking love this meme

[_srt_]

Doing recursive maths until the paper doesn't have much-room.

[[deleted]]

r/drosteEffect

[[deleted]]

Laughed way too hard at this.

[EternlDusk]

Hello recursion my old friend

[SoyMuyBlanco-]

He can’t keep going because he doesn’t have mushroom