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[Rentahamster]

Are they still doing this convoluted method when asked to do 2346-1798?

Why not?

2346 minus 1000 is 1346

1346 minus 300 is 1046, 1046 minus 400 is 646 (in your mind, the 700 is easily broken up into the quantity (300 + 400)

646 minus 40 is 606, minus an additional 50 is 556 (in your mind, visualize "90" instead as the quantity (40+50).

556 minus 8 is 548.

Done.


It's easier to do it in you head this way, than to visualize long subtraction. With long subtraction, you have to keep track of all the places all the time, whereas with left to right, you can forget about the highest place values once you solve for them. e.g. once you get to "646", you only have to think about "646 - 98" for the next step, and forget about 2346 - 1798.

 

[otapnam]

I believe the second method is much more effective because it makes more sense. I was taught the first method and clearly remember it being really cumbersome. Fortunately I have never had to use such archaic methods in years.



I would solve it like this:
1798 + 2 = 1800
2346 - 1800 = 546
546 + 2 = 548

That's just me though

Id do it that way too. My parents had a restaurant and I was taught to make change quickly that way

 

[kirameo1]

I agree with those saying that it's an easier method to do mentally, and in the long run that will be much more beneficial. It also makes more mathematical and structural sense.

 

[makingmusic476]

I've done it from left to right my entire life. It was something I've always done intuitively.

I'm 25, and I took all honors and AP math classes in school. Glad to see my oddity has been vindicated

 

[Alpha_eX]

It teaches you how to add and subtract mentally

I agree with this.

Using the classic method you're mostly practising subtraction, this way you'll be doing subtraction and addition. It's a good way to reinforce both.

I use a similar method when teaching my student, I break things down into tens, sometimes removing the zero from the end so the sum is in it's simplest form.

Try doing the classic method in your head but imagine you're a kid who doesn't get maths, it's very confusing, especially with remainders being carried over and such.

 

[Joe Shlabotnik]

Now show all your work for my example above 2346-1798

In my head:

2 - 1 = 1
10 + 3 = 13 (this is trivial, I just think 13)
13 - 7 = 6
64 - 9 = 55
556 (or just 56 and remember the hundreds place) - 8 = 548

 

[SilentRacoon]

2346
-1000
1346
-700
646
-90
556
-8
548

edit: its a variation

Well this seems much more convenient.

 

[Vermillion]

While we're here - I seem to have forgotten that new method for multiplication - I think you were supposed to go across for both or something? How does that go, again?

 

[nullset2]

What the fucking fuck. That approach to performing substractions is horrendous. It does work but it's not what a little child needs to grasp correctly such elemental concepts of math. I mean, I get it, but what the blazing fuck.

I detest fuzzy, "new wave of teaching" kind of math. What's wrong with good old math based around constant practice and memorization.

 

[PFD]

i actually do it that way in my head. i have an alarm clock which needs math problems you have to solve to snooze or turn off. and naturally in my head ive been able to solve them with quickness using the second method.

but on paper, fuck no.

This is amazing

 

[Kinitari]

Woah, that's crazy, that's how I intuitively do math. I was talking about it with the lady the other day. Guess I didn't invent the method

 

[Starfish Hero]

I agree with those saying that it's an easier method to do mentally, and in the long run that will be much more beneficial. It also makes more mathematical and structural sense.

Came here to say this. Pretty much everyone I know who's good at mental math admitted to teaching themselves addition/subtraction this way after being taught the "traditional" way.

 

[Vermillion]

This is amazing

AlarmDroid does it. Incidentally, this did not help me get up at all :/

I would put the alarm across the room, so I had to get up and solve the problem, and I would do this then go all the way back to my bed and go back to sleep.

 

[Joe Shlabotnik]

I feel like I'm taking crazy pills. I'm 36 years old. I learned the traditional method of subtraction 30 years ago, and while I was good at arithmetic I seriously doubt I'm a math savant.

This method seems obviously better and easier to me and provides a clearer idea of what you're actually doing. It's empirically a better way to estimate even if you don't go all the way down to the ones.

 

[Anteo]

i actually do it that way in my head. i have an alarm clock which needs math problems you have to solve to snooze or turn off. and naturally in my head ive been able to solve them with quickness using the second method.

but on paper, fuck no.

OMG that's awesome

 

[Fuzzy]

While we're here - I seem to have forgotten that new method for multiplication - I think you were supposed to go across for both or something? How does that go, again?

You mean this?

http://www.youtube.com/watch?v=PYrgjMubh-c

I learned this also in enrichment math in elementary school.

 

[MartyStu]

Yeah, I use a variation of the second method when I do math in my head.

Much faster, especially when estimation is good enough.

You mean this?

http://www.youtube.com/watch?v=PYrgjMubh-c

I learned this also in enrichment math in elementary school.

Personal experience taught me this one. EX:

703 * 118

703 * 100 = 70,300 +
703 * 10 = 7,030 +
703 * 8 = 5,624 +
= 82,954

 

[JohnsonUT]

My son is going into Kindergarten this month and I have already taught him the right to left method and carrying/borrowing the one. Hope I didn't screw him up for life.

 

[WrenchNinja]

Second way is easier for kids to learn and understand, I see no issue other than you being lazy and having issue with the steps. If it helps them get a better understanding, it's not a waste of time.

Doing it in steps helps the kids and teachers see how / where students are making mistakes.

Well you are right, I am lazy. Looking through the thread, this method does make sense and I guess I have been doing it this way in my head. I guess I just find it strange that they're writing it out.

 

[Sye d'Burns]

My son is going into Kindergarten this month and I have already taught him the right to left method and carrying/borrowing the one. Hope I didn't screw him up for life.

You monster. You're probably just the type that would impose imperial units of measurement on their children as well. You disgust me.

Spoiler

Right to left for life.

 

[Vermillion]

You mean this?

http://www.youtube.com/watch?v=PYrgjMubh-c

I learned this also in enrichment math in elementary school.

I think this is it! Thank you!

 

[MartyStu]

Well you are right, I am lazy. Looking through the thread, this method does make sense and I guess I have been doing it this way in my head. I guess I just find it strange that they're writing it out.

I think today's schools are being much more practical about these things.

Realistically most arithmetic that most people will ever do is mental, so they are training kids to be better at it.

 

[Alucrid]

Now show all your work for my example above 2346-1798

No.

(2346-2000)+202 = 548

 

[Fuzzy]

My son is going into Kindergarten this month and I have already taught him the right to left method and carrying/borrowing the one. Hope I didn't screw him up for life.

It'll probably help him. I have two older brothers and before I even started kindergarten I watched and learned 4th grade math from my older brother. Because I was so far ahead of all the other kids in my class they put me in enrichment math and that's where I learned the other methods.

 

[Winterfang]

I'm in Shock at how little I remember of even basic math.

 

[Rentahamster]

No.

(2346-2000)+202 = 548

I complement your work. Well done, I say!

 

[Chris R]

Its an alternative form, ideally its present alongside other methods as to differentiate instruction (showing content in multiple forms for a diverse array of learning styles). Check-out your state's Mathematics Standards and see what they require at your cousin's grade.

Checkout lattice multiplication.

Its to endow a number sense and not the systematic plug-and-chug rote maths learning.

I liked this method for a few weeks in 5th grade.

 

[Alucrid]

I complement your work. Well done, I say!

Uh...that's great and all, but where's my sticker?

 

[José Mourinho]

I feel dumb. I actually can't grasp the new method with larger numbers but can do them the old way with ease.

 

[javac]

Both make perfect sense. Everyone works things out differently. No big deal.

 

[TimeEffect]

That second method is pretty cool.

 

[WrenchNinja]

Looking into this more, I guess this is how abacus worked. And my mom was taught this way when she was a kid. I guess this is older than jesus and the classic method isn't really classic? This is mindblowing stuff.

 

[Vermillion]

Looking into this more, I guess this is how abacus worked. And my mom was taught this way when she was a kid. I guess this is older than jesus and the classic method isn't really classic? This is mindblowing stuff.

Heh, I had an abacus as a kid.

 

[SRG01]

The reason why this method is taught is because some people tend to miss the carrys during addition and subtraction. I think this method is taught at some supplementary schools (ie. Kumon?) because it's a faster way to do math mechanically.

Whether the student actually learns something out of it is another question altogether.

 

[TAJ]

How does the old way not show your work? If you can't look at the old way and see where someone went wrong, then I pity you.
But then, the idea of showing work was what eventually killed my interest in math.

 

[Kajigger]

Easiest method

 

[Anura]

When I have to multiply big numbers in my head I break them down

Lets say for an example I need 74 Times 98, I do it in chunks 10 times 98 is 980 add that together and you get 1960 add that together and you get 3920 and that there is 40 times 98

And 30 times is 2940 add that together is 6860
4 times 98 is 392 add those two and you get the answer

I usually don't do numbers like that though lol

This method for me is just easier to keep track of in my head instead of doing the whole thing like you would on paper

 

[Delicious Waffles]

During my student teaching, I saw a bunch of these whack-a-do methods of teaching the basics. I could never wrap my head around them. There's also the lattice method for multiplication, which isn't too bad.

Also, when student teaching in fourth grade, division was also mixed up a bit. For example, if you were dividing 2115 by 15, the way I learned it, you would break it down (15 doesn't go into 2 but it goes in 21, etc. etc. etc.) but now, they take the whole number (2115) and try to get as close as possible to it with 15. It was very confusing to me and, whenever I had to help students, I told them up front that I didn't get their method since I didn't grow up with it so I had to explain it to them the way I knew how to do it. Some of them found that easier than the new method.

 

[IdreamofHIME]

The 2nd way makes more sense to a child and is thus easier to explain to them, but the 1st method is much easier in the long run.

tbh, anything that gets kids better at Math. I went all through school and even graduated from a top University and I have mega trouble doing metal arithmetic. It's my biggest shame.

 

[Kitschkraft]

To be honest...this is how I tend to add and subtract things in my head, especially with "obscure" numbers.

I tend to find that using the biggest rounded numbers makes things easiest.

Random :

1547 + 439

1540 + 430 = 1970....
7+9 = 16...
1970 + 16 = 1986

I don't think it's that odd.

 

[Kitschkraft]

During my student teaching, I saw a bunch of these whack-a-do methods of teaching the basics. I could never wrap my head around them. There's also the lattice method for multiplication, which isn't too bad.

My mind is blown right now.

 

[smokeandmirrors]

lets just teach 'em reverse polish notation and be done with it

 

[Falcs]

You're all doing it wrong.
Easiest way:

Windows Key + R
"Calc" + Enter

 

[Partial Gamification]

lets just teach 'em reverse polish notation and be done with it

Knotted into quipus for homework.

 

[SystemShock2]

My mind is blown right now.

I'm in love with her handwriting and marker.

The way I do subtraction in my head is pretty inefficient I think, but it's more like reverse addition than subtraction. Say I have 45 - 29, I see that the second ones place is lower, so I do 4-2-1 to equal 1, then I know that 6 adds to 9 to make 5, so I put 6 at the end for 16. It gets harder for larger numbers, so I sometimes make an estimate and add numbers until it comes out right. It seems like a slow process, but I've got it down pretty good.

 

[Fuzzy]

When I have to multiply big numbers in my head I break them down

Lets say for an example I need 74 Times 98, I do it in chunks 10 times 98 is 980 add that together and you get 1960 add that together and you get 3920 and that there is 40 times 98

And 30 times is 2940 add that together is 6860
4 times 98 is 392 add those two and you get the answer

I usually don't do numbers like that though lol

This method for me is just easier to keep track of in my head instead of doing the whole thing like you would on paper

Holy shit you do things so complicated.

74 * 100 = 7400
74 * 2 = 148
7400 - 148 = 7252

 

[UFRA]

The second way is pretty cool, once I understood it by seeing it expressed properly.

Trying to understand the second method by having it written out in words makes it seem super complex.

 

[daycru]

When I have to multiply big numbers in my head I break them down

Lets say for an example I need 74 Times 98, I do it in chunks 10 times 98 is 980 add that together and you get 1960 add that together and you get 3920 and that there is 40 times 98

And 30 times is 2940 add that together is 6860
4 times 98 is 392 add those two and you get the answer

I usually don't do numbers like that though lol

This method for me is just easier to keep track of in my head instead of doing the whole thing like you would on paper

This is how I've always done it.

 

[K.Sabot]

Tom Lehrer should write a song about this.

 

[toastyToast]

Looks like a much easier method for a kid since they don't have to carry numbers and whatnot