How the fuck does "Common Core" work? What is this fuckery?
consider the following:
solve 15 - 11.
1) 11 + 1 = 12
2) 12 + 1 = 13
3) 13 + 1 = 14
4) 14 + 1 = 15, which is exactly what we wanted
adding up 4 of the 1's we get 4, hence 15 - 11 = 4.
Q(uickly).E(ject).D(ick).
>>7641586
So that's what that fucking lecturer was doing. Some intro maths lecturer at my Uni was trying to show something like that and everyone was confused as fuck. Didn't help that the guy was ESL.
Seems slow and pointless.
>>7641565
Common core is written mental math for retarded people that can't into mental math by themselves ( and generally it just ends up confusing them just as much if not more, as their retardation is genetic and not due to a flawed teaching method ).
>>7641565
Those two ways are literally the same thing, the second is just made more explicit. What's happening is they start at 12 then preform a series of smaller steps to reach 32, they then add up these smaller steps and that gives the difference between the two.
>But the way I learnt is easier, this is pointless.
They way you learnt it works for simple problems, when you take it to something larger, it becomes very cumbersome for mental arithmetic.
>>7641586
But where do the other equations come from? Why do they make a simple subtraction so overly complicated?
>>7641609
They can be whatever you want them to be, for example if I was doing what OP posted then I might have done it like:
1) 12+8=20
2) 20+12=32
But you could have thrown in an extra step, if you wanted, and done
1)12+8=20
2)20+10=30
3)30+2=32
Or perhaps
1)12+10=22
2)22+10=32
Alternatively you could have done
1)12+20=32
You can brake it down into as many (or as few) smaller subprocess as you want.
>>7641614
Ok. Weirdly the way I first heard about it was that you broke it up so that you always ended up with a multiple of 10.
So if it was like how I heard then OP's example would've been
12+8=20
20+10=30
30+2=32
Or
12+18=30
30+2=32
Depending on how derp the person doing it was.
Why base 10 and not base 12?
>10
>divisible by 1, 2, 5 and 10
>12
>divisible by 1, 2, 3, 4 and 6
What's so special about 5? Do people just like prime numbers? Do they like 10 because you can divide it by an odd number?
>>7641624
Look at your hands anon, that's the reason people like base 10.
>>7641626
I have 9 fingers you uncaring bastard.
Has anyone in the last millennium even used their fingers for counting?
>>7641629
>Has anyone in the last millennium even used their fingers for counting?
Yep, we call them children.
>>7641632
Huh, I thought that was a TV-only thing. None of the kids in my family were taught to count like that.
>>7641633
I think you'll find most children are taught like that. Out of curiosity, how were you taught?
>>7641636
With words, one, two, three, four etc.
If we counted something it'd be circles drawn on paper or something like that. Also eventually used things like pic related for doing units vs tens vs hundreds.
>>7641619
This is how I do math mentally, only with much larger numbers (32-12 would be one step, easy).
I get what they're trying to teach children, but I don't think you can teach a thought pattern, like that, effectively on paper.
The way I learned to do this was by having tests that made us solve sets of about 50 simple addition and subtraction problems.
It just happens if you can do it, if not, you're just adding more ways for kids to be confused about math.
The idea is to regroup your numbers into things that can be easily done in your head, multiples of 5s or 10s or whatever. It's how everyone who is any good at mental arithmetic does it.
All the people who bitch about common core simply don't understand it. They're like programmers who still refuse to code in anything but assembly, using nothing but algorithms that were devised back before the transistor was invented.
In the subtraction problem shown, it's taken that it's easier for most people to add than to subtract. So you start at 12. Add 3 to get to a multiple of 5. Add 5 to get to a multiple of 10. Add 10 until you get close to the answer. And then add whatever's left.
Do it in your head. "12, 3 (makes 15), 8 (makes 20), 18 (makes 30), and 2 gives 20."
But maybe you're not convinced by small numbers. Try it with 73299 - 4573.
4573, 2 makes 4575, 7 makes 4580, 27 makes 4600, 427 makes 5000, 5427 makes 10000, 65427 makes 70000.
> at this stage, the problem is reduced to adding 65427 and 3299
> I'd add 3300 and subtract 1
> common core teaches you to think about how it works, so you can invent improved methods like that on the fly
65427 + 3300 = 68727, minus 1 gives 68726
You can do it in your head, without risk of error from carrying (which is really counter-intuitive to a lot of people), and you can do it with really big numbers.
>>7641656
Now, a person well versed in this method will come up with their own optimizations, things that are easy and intuitive for them. It's not one size fits all. It's not supposed to be.
73299 - 4573
> I can happily see that 4573 > 3299, so I'll start by adding 60000. Actually, I like to subtract here, for reasons that are my own. It doesn't matter. It's flexible.
I say "6"
> and I am left with 13299 - 4573
> I want to add 13 - 4, but see that 573 > 299, so I only add 13 - 5
"8"
> and I am left with 1299 - 573
> actually, I'm just going to do 1300 - 573, then subtract 1 at the end. I can do this in my head directly, but for completeness I might count like this if I'm tired or something.
> 573, and
"7"
> makes 1273, and
"2"
> makes 1293, and 7-1 is
"6"
"68726"
It gets even better when you start doing multiplication, division, or roots. Can you calculate 5th roots in your head? I can, and I'm kind of a dumbass. But it's all the same idea.
are you all fucking retarded?
if I want to calculate 86 - 32
32 + 8 = 40
40 + 40 = 80
80 + 6 = 86
so it's 54
they just added in a step to get to the 5 so it's even easier.
it's not slow, it's not "fuckery".
it's intended for doing substraction in your head and it's a great method.
I mean, who doesn't do it?
when i substract I imagine this in my head.
>>7641724
reakky? when I do subtraction in my head I do it like long subtraction.
maybe you're special
>>7641749
>2015
>Using such an inefficient method.
Any you call other people special.
>>7641604
This. Anyone who can into mental math will confirm that you already do the second way, just much faster, with less babby steps.
>2196 - 1812
>96-12 = 84
>21-18 = 3
>Ans. 384
Who gives a shit? It's fucking math. Why bother learning anything but the very basic? Computers and nerds can do the rest, it won't have any use for 99% of the population.
Seriously, when the fuck does algebra come into play for the vast majority of humans? It's the equivalent to speaking Mongolian.
>>7641941
here is your reply
The way I see it is common core is just an overcomplicated form of doing math by rounding.
Like, if you want to know 76x4. You do 70x4=280 and 6x4=24. So 76x4 is just 280+24=304. OP's example is for substraction but it's the same concept.
You're asking kids to use laws of distribution before they learn fucking multiplication.
Consider the following:
Prove A-B=C
Let A>B
Let Sn be the sum of two numbers
Let An be some arbitrary number
B+S1=A1
A1+S2=A2
A2+S3=A3
A3+S4=A4
...
An+Sn=A
Sum(Sn)=B-A=C
COMMON CORE IS NOT A CURRICULUM
AGAIN
COMMON CORE IS NOT A CURRICULUM
Common Core is a set of standards; that's it. It is a guideline for establishing what kids should know/be practicing in what grade.
You can see the goddam standards for yourself:
http://www.corestandards.org/Math/
NOWHERE does it dictate HOW the standards should be taught; only that they should be.
If some pants-on-head liberal douchebag wants to teach kids how to add and subtract in the most dumb-ass way possible, that is the prerogative of that teacher/school/district.
Personally, if my kid brought this home, I'd show them how I did it, then let them figure out which method they liked better. And if the teacher threw a fit, I'd pull my kid out of that school and find someplace that doesn't treat children like retarded monkeys.
