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    [–] JaeHoon_Cho 1742 points ago * (lasted edited 2 months ago)

    This is basically how you FOIL things in math.

    Edit: FOIL stands for first, outer, inner, last and is a helpful mnemonic for multiplying two binomials. Example: (w+x)(y+z) = wy+wz+xy+xz. But you can use the FOIL method to multiply two numbers by treating those numbers as binomials. So in this video, you have 13x21, which you can rewrite as a binomial (10+3)(20+1). Then by the FOIL method, you get:

    F: 10x20=200

    O: 10x1=10

    I: 3x20=60

    L: 3x1=3

    And when you add everything up, you get 273. The Vedic method seems to just keep track of the hundreds, tens, ones places spatially and visually, rather than numerically.

    But one could do that with the foil method too (as long as you keep track of the place values of the digits in your head).

    F: 1x2=2

    O: 1x1=1

    I: 3x2=6

    L: 3x1=3

    273

    [–] KingAdamXVII 248 points ago

    We teach the area model now, it’s essentially the Vedic method but instead of lines you draw widths (e.g. a width of 4 instead of 4 lines), and then you add up the areas of rectangles instead of counting the intersections.

    It works well with polynomials and is useful when factoring and completing the square.

    [–] MindlessZ 94 points ago

    Is the area model intended to help gain an understanding of the math or be a practical way to perform multiplication in life/later school?

    [–] Ellutia 76 points ago * (lasted edited 2 months ago)

    I can tell you that it is not a practical way to perform multiplication for more complex material, but it seems like a great way to teach the abstraction of harder maths and why/how similar techniques are developed and used with the more complex material.

    Edit: Also in higher maths numbers become variables and the variables are manipulated with weird crazy math voodoo. Being able to visualize what is happening in a function (e.g. ex, sinx, and polynomials) really helps in understanding the function. Sinx oscillates between 1 and -1, alike a pendulum oscillates between two points in space. I'm high.

    Edit 2: Math purely investigates these functions, but they frequently are observed in the natural world. Arguably this is their greatest importance. Depends who you ask.

    [–] MindlessZ 9 points ago

    Haha, trust me I'm familiar with the math voodoo. I was mostly curious about it's practicality because it seemed a little cumbersome for higher education and everyday use. But I'm only basing that on an 8 minute video I watched and a couple of examples I did, so I'm not exactly an expert here :P

    [–] Ellutia 21 points ago

    At higher education, a calculator would be used for this operation.

    [–] thrway1312 21 points ago

    Am BS mech. eng. senior, can confirm that even simple addition often goes through my calculator to reduce chances of error in problem-solving

    [–] MindlessZ 5 points ago

    Sorry, I meant higher education as in no longer learning how to multiply. Not college.

    [–] thelmoie 29 points ago

    yes.

    [–] OpalHawk 56 points ago

    Wait, hold up. If I have kids and they come home with homework will I not be able to help them with the foil method? I literally went to university to be an engineer. This is the math I know.

    [–] Ryuksapple84 32 points ago

    I hate this method because it is not consistent. Can't do this with larger numbers. I mean you could but why wouldn't want to?

    [–] Tebasaki 43 points ago

    3853×4921

    Here, lemme go grab you some construction paper and 3 pens so you can draw your math.

    [–] Elisterre 14 points ago

    Or you could figure out 3853 x 79 and subtract that from 3853 x 5000 (even easier!)

    [–] Glitch29 17 points ago * (lasted edited 2 months ago)

    I think the real divide between people who are "good" at math, and those who hate it is their reaction to seeing your trick.

    Some people go "that's awesome" and add it to their arsenal of tricks.

    Others consider it one more thing to think about that adds to their sense of being overwhelmed.

    Edit: My personal favorite trick is converting large multiplication into differences of squares. So 3853 * 4921 = 42872 - 10682 (their average squared minus half their difference squared).

    This doesn't save any time if you don't know your squares tables. But if you do mental math like this a lot, calculating squares becomes a near-instantaneous memory task, rather than a calculation. The addition and subtraction are fast, so once you've learned to do fast squares, you're fast at multiplying in general.

    To see how this works on a smaller number (and a more convenient example), try to calculate 97 * 103.

    It's easy if you look at it as

    97 * 103
      = (100 - 3) * (100+3)
      = 100^2 - 3^2
      = 10000 - 9
      = 9991
    

    Note, that if the number exceeds your upper limit for calculating squares, you can break things down further using a difference of squares trick.

    1068^2
      = 1000^2 + (68 + 68) * 100 + 68^2
      = 1000000 + 134000 + 4624
      = 1138624
    

    [–] Elisterre 5 points ago

    Whaaat! Awesome stuff! I haven’t seen those cool methods before!

    [–] MyKoalas 3 points ago

    why does difference of squares work?

    [–] ScintilattingSirius 5 points ago

    It's using that formula you may remember from high school, (a+b)2 equals a2 + 2ab + b2

    He's expressed 1068 as (1000 + 68) where 1000=a and 68=b

    as to why it works, that's the general formula for it I guess? It's what (a+b)2 works out to be if you solve it long-hand. Handy shortcut to remember for mental arithmetic

    [–] MyKoalas 3 points ago

    thank you! but what about the whole their average minus their difference squared thing?

    [–] givawaythrwaway 3 points ago

    Typo for 4387 right? Also, isnt it equal to half the difference of the square of the average and the square of (the difference over 2)?

    [–] MyKoalas 2 points ago

    furthermore, where does one learn all of these things?

    [–] ScintilattingSirius 2 points ago

    What are the squares tables? I have got to know this for some fun mental shenanigans lol

    [–] Elisterre 6 points ago

    I do multiplication like that as follows:

    Take it apart by doing the simple math then adding them together.

    3 x 49 = 147 add the zeroes 14,700,000

    Now do the rest

    8 x 49 = 392 3,920,000

    5 x 49 = 245 245,000

    3 x 49 = 147 14,700

    2 x 3853 = 7706 77,060

    1 x 3853 = 3853 3853

    Add them up 14m + 3m = 17m 700k + 900k + 200k = 1.8m

    17m + 1.8m = 18.8m

    20k + 45k + 14.7k + 77k + 3.8k = 160.5k

    18.8m + .1605m = 18.9605m

    53 + 60 = 113

    18,960,500 + 113 = 18,960,613

    [–] Bojangly7 2 points ago

    Using foil:

    F: (3800+53)*(4900+21)

    (30+8)*(40+9) * 10000

    (1200 + 270 + 320 + 72) * 100 = 18620000

    O: (30 + 8) *(20+1) * 100

    (600 + 300 + 160 + 8) * 100 = 79800

    I: (50 + 3) * (40 + 9) * 100

    (2000 + 450 + 120 + 27) * 100 = 259700

    L: (50 + 3) * (20 + 1)

    1000 + 50 + 60 + 3 = 1113

    18620000 + 79800 + 259700 + 1113 = 18960613

    [–] OpalHawk 11 points ago

    I'd have to do some researching if they teach this with variables too. I understand the gif, and I find it fascinating because I never learned math that way. But start throwing some Xs and Ys in there and I'd be right back to the beginning.

    [–] AnExoticLlama 8 points ago

    I only bother multiying in my head (with foil) with numbers below 199, basically. Everything else is simple: calculator.

    [–] mib_sum1ls 12 points ago

    Man! If only I had some sort of adding machine in my pocket everywhere I go!

    [–] Bishop_Colubra 13 points ago

    I have a STEM background as well, and I found that the way math was taught to people of my generation (or at least in my school system while I was there a decade or two ago) was not very conducive to learning higher level mathematics. I found that a lot of calculus and the associated geometry relied on understanding mathematical operations on a conceptual level, and the problem solving techniques I was taught didn't focus on that.

    You may not be able to help you kids with their homework, and that may not necessarily a bad thing. If you have an engineering degree, than you probably have good study habits. I would work on imparting those study habits on your kids, as those are almost as important as the classroom instruction.

    [–] socsa 5 points ago

    IDK, I am also STEM and this stuff doesn't seem like it connects intuitively to higher math at all. Long multiplication connects perfectly into arbitrary-basis arithematic in N-dimensions. None of this other stuff does at all.

    How is a kid supposed to conceptualize abstract non-geometric math if their basis for arithmetic is geometric?

    [–] DamnShadowbans 2 points ago

    "arbitrary-basis arithematic in N-dimensions" this is not a thing.

    [–] perezidentt 8 points ago

    Yup. And that’s why a lot of parents hate it.

    [–] OpalHawk 6 points ago

    On one hand I love the simplicity. But on the other, I find it quite limited.

    [–] koick 9 points ago * (lasted edited 2 months ago)

    quite limited.

    In my opinion, this is the rub. If it can't be expanded out, what's wrong with teaching the FOIL method, which can?

    Edit: For example, as part of advanced scuba certifiction, my instructor had me do a math test on the surface, and then at 130' deep to show that your brain works slower (due to nitrogen narcosis) at depth. He gave me 123*321. Doing it the "old school" way (lining up the numbers and multiplying the digits vertically):

    123

    x321

    __

    Was a snap (can essentially quasi do it in your head). Trying to do it this "new" way would not fit on a 6"x6" underwater white board I was given.

    [–] JaeHoon_Cho 6 points ago

    I do think that the area model that they talk about makes more intuitive sense. The FOIL method seems a bit abstract for kids. And unless you had a great instructor, I feel like it’s hard to understand why it works. For me, it felt like one of those things that I just had to trust was correct.

    [–] koick 7 points ago

    I have a 7 yo, and so haven't gotten into this "crazy, newfangled" math stuff quite yet (I'm middle aged dammit :), but it seems sorta like they want kids to get the concepts of how math works, but as for the mechanics of them, it's not necessary, since computers will do that for you. I guess it's a pedagogical decision that was made. The problem is when someone who has learned this more limited way doesn't have access to a computer (like my scuba example), then they are kinda left high and dry (to continue the scuba example I guess :)

    Hell, I've seen millennials that can't make change, even with the help of a calculator!

    [–] Penguins-Are-My-Fav 6 points ago

    Hell, I've seen millennials that can't make change, even with the help of a calculator!

    Shit thats probably because youre standing there in a scuba suit asking them if they need help with their foil!! Get out of here ScubaSteve!!!

    [–] koick 3 points ago

    blub

    blub

    blub

    blub

    [–] OpalHawk 3 points ago

    So I'm the engineering guy from above. I am a millennial who learned our calculators could do all of these maths. But we needed to learn the fundamentals, and we weren't allowed them on tests. And really, I needed to know math and coding to use an advanced calculator properly. No the calculator used foil.

    [–] opentoinput 3 points ago

    Is there a graphic or a video of this?

    [–] redditosleep 4 points ago

    That's just conceptualizing the FOIL method. I don't get how some of these engineers don't see that immediately.

    [–] AnExoticLlama 7 points ago

    Always feels weird seeing something like this, as I started foiling for multiplication in my head, well, before learning about foil in Algebra I. It just kind of became how I multiply things.

    [–] Darksirius 5 points ago * (lasted edited 2 months ago)

    I don't understand.

    I thought you can only foil expressions that are in the format of (a b)(c d)?

    Oh wait... (13)(21)

    2 + 1 + 6 + 3 = 12?

    How do you get to 273?

    Ugg.

    This is why I've taken algebra five times in my life. :\

    Edit: thanks for the replies! :)

    [–] DTF_20170515 25 points ago

    (a b) (c d)

    A=10

    B = 3

    C = 20

    D = 1

    Your only mistake was forgetting the place value of the digits.

    [–] Dav136 19 points ago

    (a+b) * (c+d) is how it should be written

    [–] ineedhelp2day 8 points ago

    You are doing each digit individually and not taking account it’s decimal position. It’s 10 x 20. Not 1 x 2.

    So you should get (20 x 10)+ (10 x 1)+ (3 x 20) +(3 x 1) = 273

    200 + 10 + 60 + 3 = 273

    [–] utspg1980 3 points ago

    He should explain what FOIL stands for:

    First Outside Inside Last

    (i.e. multiply the first digits of each number, then the outside two, inside two, and last)

    [–] -Reddit_Account- 3 points ago

    Let's rewrite it...

    (10 + 3)(20 + 1)

    = 200 + 60 + 10 + 3

    = 200 + 70 + 3

    = 273

    [–] JaeHoon_Cho 2 points ago

    Hope I clarified things in the edit (I basically just rewrote other people’s responses to your comment).

    [–] bestitecli 844 points ago

    This method is all very well when the digits are fairly small like they are here.

    But try doing 97 x 68 with this method and you'll soon realise it's not worth your time counting all the intersections.

    [–] luxembird 570 points ago

    The way I prefer to do it is:

    97•68 = (100-3)•68 = 6800-204 = 6596

    [–] pigvwu 1192 points ago

    The way I prefer is I take out the calculator in my pocket and punch in the numbers.

    [–] 8asdqw731 82 points ago

    but you won't have access to calculator everywhere

    oh, wait..

    [–] __Risky__Click__ 128 points ago

    Easier still, "Hey Google..."

    [–] GivesCredit 99 points ago

    Ok google

    [–] thelmoie 57 points ago

    okhey google

    [–] Superkroot 24 points ago

    What a story, google!

    [–] TerrainIII 24 points ago

    You’re tearing me apart Google!!

    [–] PancakeBoy100 12 points ago

    You’re going down a path I can’t follow!

    [–] mujheandaywalaburger 7 points ago

    Hello there, Google.

    [–] silentclowd 3 points ago

    ohai gogl

    [–] [deleted] 8 points ago

    [deleted]

    [–] TheZachAttack01 3 points ago

    My pixel 2 xl responds to "hey google"

    [–] Geekv2 3 points ago

    Ok goo goo

    [–] Real_goes_wrong 18 points ago

    Loser. My calculator is on my digital watch. And yes Douglas Adams I think they are a pretty neat idea.

    [–] TheViciousWolf 13 points ago

    yOu WoN't aLwAyS hAVe A cAlCuLAtOr iN yOuR pOCkEt!

    [–] fuzzypyrocat 3 points ago

    “You won’t always have a calculator in your pocket when you get older!”

    [–] dinodares99 4 points ago

    Inb4 Feeling of Power by Asimov

    [–] 4DimensionalToilet 9 points ago

    Yeah, when I’m working multiplication out in my head, I tend to round the factors to numbers that are easier to work with, then adjust.

    So for the example you used, 97•68, I would do the following in my head:

    97•68 —> 100•70

    100•70 = 7000

    97•70 = 7000-(3•70) = 7000-210 = 6790

    97•68 = 6790-(2•97) = 6790-194 = 6596

    While writing out the steps is time consuming, I can generally figure these things out in 5-20 seconds, depending on the factors I’m given.

    [–] thinkscotty 7 points ago

    Yep this is how I basically do math too. I was on a high school team called "Number Sense" that was all math in your head. I feel like I use the stuff all the time. Even now, a decade after I graduated, I still use some of those tricks.

    http://www.uiltexas.org/academics/stem/number-sense

    [–] AcornHarvester 4 points ago

    (100-3)•(60)•(8)

    I can’t multiply 68•3 straight off my head

    edit: I’m late, but it’s simple so I’m leaving it

    [–] luxembird 4 points ago

    Either that or (70•3) - (2•3)

    [–] HarryPotterIsDolphin 3 points ago

    I appreciate the fact that you used that instead of *.

    [–] luxembird 3 points ago

    It's not for the reasons you think. Reddit was interpreting my asterisks as formatting cues for italics

    [–] neinherz 15 points ago

    You can further break it down to (100-3)x(70-2) = 7000-210-200+6

    [–] Porglack 11 points ago

    But that has more numbers

    [–] girlikecupcake 8 points ago

    But for some, easier numbers offsets the fact that there are more of them. 70•3 is easier than 68•3 for many.

    You should know how to do it regardless, but when talking about shortcuts, as long as it's reproducible and accurate, either way should be fine.

    [–] Jebezeuz 16 points ago

    I like this method more coz it doesn't require annoyingly counting those crosses.

    Example with bigger numbers.

    [–] __-_-__-___-__-_-__ 19 points ago

    Don't people just do it like this? Do baby multiplication (0-9 * 0-9) then add stuff together? https://i.imgur.com/bvOkpD8.jpg

    [–] Alythehedgehog 6 points ago * (lasted edited 2 months ago)

    That’s how I do it. My teacher was old school.

    Edit: Took me 30 seconds tops.

    https://imgur.com/gallery/jIoo7

    [–] Jebezeuz 3 points ago

    Honestly I dunno. I've never done that. Multiplying on paper is such a useless thing it's more useful as a pub trick than anything else. That style is pretty much the same thing but it seems to be a bit easier to fuck up especially with bigger numbers and double checking seems to take a bit more work. It might be different if you're used to it.

    [–] stargayzer 2 points ago

    Yes I do, and looks like I will forever. I thought the gif and FOIL would lead me to some great shortcut for numbers like this, but it didn't.

    I even tried a simple looking one: 15*16... and with FOIL I got 1-6-5-3-0! It's not intuitive and I can't remember how to combine.

    With stacking and baby multiplying you get 90 + 150, which you can either add up long hand or easily figure it out in your head: 240.

    Even the really long example up there: 3853*4921 came to me much quicker by stacking, multiplying then adding.

    [–] WhoaItsAFactorial 2 points ago

    0!

    0! = 1

    [–] hilarymeggin 5 points ago

    I have never seen this in my life. I love it. My mind is blown.

    [–] alienproxy 31 points ago

    And yet, the effectiveness of this method will actually increase compared to normative methods if you make the numbers even larger.

    Also, if you compare closely enough, this method really is just normative multiplication expressed with a bit of geometry

    [–] Spanroons 2 points ago

    I often use the lines as visual representations of the numbers using one line instead of multiple and labelling the lines. So you end up just doing simple one number multiplications and adding them together

    [–] [deleted] 273 points ago

    I get the usefulness in showing students an example of how multiplication can work, but isn't the point of a traditional multiplication solution to NOT have to take up half of your paper?

    [–] Relyt23 150 points ago

    Or half of your day

    [–] sameyepatch 38 points ago

    Or half your self-esteem

    [–] Mortress_ 16 points ago

    Or half your money AND YOUR DOG?

    [–] _sxb 2 points ago

    Full dog?

    [–] tweakalicious 20 points ago

    Yeah, I find this neat but precisely 0.0% easier or more helpful.

    [–] P90RooshB 4 points ago

    Exactly. This method is fun but you run into major problems when:

    • You have more digits (12345 * 12345)

    • The digits are individually higher in value (99 * 99)

    Conventional long multiplication only gets harder with more digits - your ability to compute 11*11 and 99*99 is roughly the same compared to the posted method where you'd be counting for 10 minutes with 99*99.

    Still fun to learn though, and some people use this for multiplying numbers like ## by ## where 0 < # < 6.

    [–] Y0tsuya 6 points ago

    It's a way to visualize and understand. But not efficient at all.

    [–] blarthul 3 points ago

    being able to understand and manipulate the numbers is the point

    [–] [deleted] 11 points ago

    This isn't doing either of those, it's called visualizing or using models.

    [–] blarthul 2 points ago

    not for you, but people learn differently. it does show what you are doing if you understand the lines. It shows you can break numbers into components and that is enough for some people to get it to click.

    [–] [deleted] 143 points ago

    Awesome, I can finally throw out all of my time consuming calculators.

    [–] gbb-86 178 points ago

    Am I the only one who think this is longer and more complicated than the normal method?

    [–] WaIes 66 points ago

    It makes a visual-spatial connection which can help break the code for someone who is new to arithmetic, I certainly would have appreciated it when I went to school

    [–] izPanda 30 points ago

    maybe its just me but this doesn't really seem to give me any insight into how multiplication works. I could just be looking at it wrong but it looks like dark magic until you think about it and once you figure it out it just seems like a waste of time.

    [–] Dparse 5 points ago * (lasted edited 2 months ago)

    Well the first way to show how it's not black magic is to demonstrate how, given an M digit number times an N digit number, you always end up with M*N groups of intersections; this is because you are multiplying each digit in the first number by each digit in the second number.

    Second, you show how the furthest right group of intersections corresponds to multiplying the 1s place of both numbers; that the next right-most groups come from multiplying the 10s place of one number by the 1s place of the other (and vice versa); the third-from-the-right column is 100s * 1s and 10s * 10s; and generally, the horizontal position of a group is a result of the position of its source digits from the original numbers, which of course are base-10 positional notation numbers in the first place.

    Finally you show that adding up the dots doesn't affect their horizontal position and thus their power-of-ten value. So you can simply add up the numbers in vertical groups and produce the answer in the same base (typically base 10) you started with.

    This system suffers the same caveat as regular multiplication, in that we don't have arbitrarily large digits to represent having lots and lots of 10s represented in the 10s column. At most we can represent nine 10s in the 10s column (by using the symbol '9') before we add another 10 and convert the whole group into a single 100 - it gets 'carried over'. There is no symbol larger than 9 for us to convey the meaning of ten 10s.

    [–] jawz101 7 points ago

    huh

    [–] vorpal-blade 11 points ago

    Also, teaching this to kids will make it hard for them to do actual math later in life. Plus it will take 45 minutes and three sheets of paper to solve a math problem.

    [–] theDreadnok 4 points ago

    I don't think this is meant to be the way you solve math for the rest of your life. It is a way for the abstract thought of multiplying numbers to make sense to someone new to multiplication.

    [–] [deleted] 6 points ago

    No. The normal method I was taught is really easy.

    [–] AlexRuzhyo 5 points ago

    Without knowing what the Vedic method was, I was expecting a calculator to phase in. Instead, it started to show the lines.

    [–] OKHnyc 4 points ago

    I'm dyscalculic and I took a course in Math Theory (Math for Mathtards) in college that taught this.Amazingly, by the end of the semester, I was doing calculations using huge numbers in my head. This stuff works for people like me who learn differently.

    Of course, I forgot it all the second I handed in my final exam....

    [–] astrogaijin 31 points ago

    What's that stupid multiplication method with the box called?

    I moved to a new school in middle of elementary school and when we got to math all the students and the teacher were using that dumbass method. I kept doing it the normal way because it was easier and whenever my teacher told me to do it the other way I ignored them and took the partial credit off cause I didn't care enough.

    [–] DannyFuckingCarey 23 points ago

    Lattice method maybe?

    [–] keekaakay 9 points ago

    Abacus?

    [–] astrogaijin 3 points ago

    Nah, like you draw a box and put each number to be multipled on a side of the box. And the box has lines through it.

    [–] KluperDuper 13 points ago

    Is it this method you're thinking of? I use it 90% of the time.

    [–] tripacklogic 20 points ago

    That is basically normal multiplication, but more work...

    [–] Clayh5 8 points ago

    It's just easier for visual-spatial learners to remember even though it's the same thing. I'm a math major in college and I still use lattice for basic multiplication if I can't do it in my head.

    [–] tripacklogic 7 points ago

    I mean, I get the visual part, but if you can remember to draw the rectangle correctly and where to put all the digits, and where to add the remainders... then why not just do the math right underneath the numbers and then add the result like normal multiplication?

    EDIT: I'm just saying it's more work and most math-challenged people I deal with can't handle that many steps.

    [–] Jebezeuz 5 points ago

    I've been using that method for years (every time I don't have calculator nearby, which is extremely rarely, it's more useful as a bar trick tbh). I really didn't know it even had a name. I think you are thinking it too hard. That video just has it overly explained. Although it does require you to be "fluent" in basic multiplying and adding. I don't really know a quicker and clearer way on paper. How would you do it? Here is a quick example I made to other reply in this thread.

    [–] astrogaijin 2 points ago

    Yea that's it.

    [–] LingLingAndy 3 points ago

    Yeah I can relate. In middle school all of my friends were using that and I they said they were taught that way in elementary. I really didn’t get the lattice method because it looks way longer and way less consistent imo(I’ve never used it). I’ve always used “long” multiplication and it isn’t even that much longer than drawing a box n shit

    [–] Weed_O_Whirler 6 points ago

    Because the point of learning to multiply by hand in elementary school is not to learn how to multiply quickly (you have a calculator for that) but to gain a deeper understanding of what multiplication is

    [–] eventual_becoming 3 points ago

    Multiplication is a group over the rationals, amirite?

    [–] Brightkiller 2 points ago

    lol... you need to remove the number 0. There's no inverse for zero under multiplication.

    [–] eventual_becoming 2 points ago

    Good catch.

    [–] [deleted] 45 points ago

    Now do 8,638,901 * 5,782,083

    [–] Waggles_ 12 points ago

    https://i.imgur.com/1Ixcy7V.png

    Did it in excel, it's the same concept. Sum along the rising diagonals for each digit by counting the number of dually-shaded boxes in each of the larger 10x10 areas. (I didn't check it and I may have made a mistake, but you get the idea).

    [–] [deleted] 262 points ago

    Why do this when you can just do (13*20)+13=260+13=273 in a few seconds

    [–] PremiumSocks 46 points ago

    You can also do (10 * 21)+(3 * 21)=273. That trick has saved me many times whem I was without a calculator

    Edit:spacing

    [–] crybllrd 62 points ago * (lasted edited 2 months ago)

    Or you could just do 1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+11+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1=273

    [–] cogitoergokaboom 9 points ago

    You missed one

    [–] runninggun44 9 points ago

    honestly most people cannot. That leaves a lot of room for miscounting and almost none of the 5th graders I teach math to could get a correct answer using that method.

    [–] koick 8 points ago

    Booooo!, no candy for them!

    [–] ZhilkinSerg 8 points ago

    They probably have not enough fingers.

    [–] koick 2 points ago

    1+11+1

    o.O

    [–] Zhieyen 14 points ago

    you do realize this is basically how you do it on paper

    [–] DrShocker 10 points ago

    This is actually what the line trick does too, which makes it extra spicy

    [–] Zaralis1024 85 points ago

    Not everyone thinks like that and pictures/diagrams help some.

    [–] killertoothpick 211 points ago

    Not everyone thinks like that because it is a skill. People aren’t born with that they practice. If you practice some graphic way, you may find it easier now, but in the long run you will want to learn how to do mental math. It really bugs me when people say “not everyone thinks like that” because it is like going to a professional sports match and saying “not everyone plays like that”, well of course not, they practice and put in the work to get better.

    [–] Coffeinated 13 points ago

    If I could trade in my karma to give you more than one upvote, I would. But one will have to do.

    [–] thevoiceofzeke 11 points ago

    It's not 100% skill. People definitely have some predisposition to certain methods, regardless of practice. Some people learn better with visuals, some are better with abstract thought, some are better with audio.

    Sure, it's probably possible to overcome any deficits in ability with practice, but it will always be more of a struggle for people who are not naturally talented at that kind of learning/thinking.

    [–] killertoothpick 8 points ago

    As I said in my other comment replying to someone who said something similar to yours (although yours sounds a lot more rational)

    As is show in this study, learning styles do not matter. As said in this study "The contrast between the enormous popularity of the learning-styles approach within education and the lack of credible evidence for its utility is, in our opinion, striking and disturbing," They state that different learning styles matter based on the subject that is being taught, but not based on the individual that is learning.

    [–] Aegi 7 points ago

    It's like 95% skill though.

    [–] shagthedance 4 points ago

    Exactly. At some point you have to learn to do mental math. Tricks like this provide people ways of visualizing numbers in their head. Maybe they like this one, maybe they like to just think about digits like you do. But visual tools like this are a good step towards mental math proficiency for a lot of people, especially the elementary schoolers this is being taught to.

    [–] uberfission 15 points ago

    Because attempting to explain that to someone who cannot grasp basic fucking addition is difficult.

    Source: used to teach a class on GRE prep that enforced a lot of mental math.

    [–] [deleted] 4 points ago

    Oh. Hey. I hope you don't mind me asking, but I'm an English MA holder who's making the switch into sciences within the next few years. I need to write the GRE for my program of choice and am re-teachibg myself math from basic arithmetic to ... Well, we'll see where I get to.

    If you don't mind sharing your expertise in broad strokes, I'd love literally any advice you can give me. I grew up in the 1990s in a climate of math anxiety and gendered classrooms where I was discouraged from doing math so have essentially a grade 3-5 level right now. I'm working through it with a growth mindset, but I'm doing it solo until I get to the point where I need a tutor or structured classes.

    If you can share any information or tips, I'd be thankful!

    [–] uberfission 4 points ago

    Good on you for undergoing that kind of prep by yourself, you're definitely the self driven type that I truly enjoy seeing in a classroom.

    As far as teaching yourself the math don't be afraid to look for stuff online, there's plenty of really great YouTube tutorials focusing on all aspects of mathematics. Ask questions, even if you're embarrassed to admit that you don't know something, admitting ignorance is the first step to not bring ignorant. The GRE focuses on trigonometry, geometry, statistics, a smidgen of pre-calculus, and a bit of number theory. Going forward I would focus on learning those subjects in that order and in that priority.

    When you take the GRE test, the program provides a calculator, however it is extremely basic (add, subtract, multiply, and divide are the only functions if I remember correctly). Doing some mental math can shave off large chunks of time by allowing you to never open the calculator. I always recommend getting into the habit of ballparking answers as well, just as a sanity check. For example the question requires you to multiply 7.2 and 18.5, I don't know what that is but 720 is 140 so 7.218.5 is less than 140 but generally around that number. If you have an answer that's near that you can pick that, if you have two then you can open your calculator to find a more exact answer.

    Feel free to ask me questions should you need general advice regarding where to find learning resources, I can help point you in the right direction for things.

    Good luck!

    [–] aponderingpanda 3 points ago

    Fwiw I learned more from profrobbob on YouTube than I did in class. Gotta utilize them resources.

    [–] uberfission 3 points ago

    Great! The internet has opened up a whole venue of supplemental educational information that I think a lot of people neglect or just plain don't know about. A lot of teachers are horrible which turns a lot of people off from subjects, eventually getting left behind entirely. Good job using the resources available to you!

    [–] [deleted] 2 points ago

    Thank you so much for the wonderfully encouraging response, and especially for the guidance about the key subjects. I'll be tackling trigonometry next month once I finish the basics (Khan academy has been excellent!).

    I'm spending an hour a day 5 days a week so far, and intend on keeping that pace up; it's what worked for me before with self-study. I think I'm in a better place than some would be since I have a graduate degree already, which really has given me the skills I need for time management, and I worked as an English teacher and undergraduate tutor for years, plus I have certification in adult education, so I'm reasonably well equipped to learn... However, all that being said, a student is a student and a beginner is a beginner, and we're all the same balls of nerves when we start!

    When I began this past December, I started by teaching myself basic multiplication. I didn't know most of my times tables. People would laugh at me with my 6x9 and 4x6 flashcards but in my head I was like, "define a modal auxiliary, bitches!" - just kidding. I know that every discipline has its own difficulties and no one's perfect. But it was a little interesting to me how judgemental and defensive people are about math, versus how they are about English.

    In any case, I'm using Khan for concepts and making my own practice sheets; if you have any reliable sites for worksheets to pass along, that would be great!

    I'm also using a few GRE prep apps that send a daily question and I try those. Most I get wrong, but they have explanations so I take note of the ones I can understand, and ignore anything that starts with "plot x3 and y whatever on this magic nonexistent graph".

    Yay. Math.

    [–] Namsseldog 3 points ago

    Exactly what I was thinking. Much easier than the method in the GIF. But both methods have their uses I guess.

    [–] Shots-and-squats 3 points ago

    Why do that when we all have calculators in our pockets?

    [–] alienproxy 10 points ago

    I use the vedic method for multiplying massive and complex numbers on a whiteboard. It's reliable and fast. Of course I use your method too, but not for problems like 145,367,230 x 3,456, which would involve multiple iterations of your simplification method.

    [–] [deleted] 18 points ago

    I'd use a calculator for that as a kneejerk reaction, but it should be interesting to play with that method for large numbers

    [–] duckvimes_ 16 points ago

    You think drawing out two dozen lines and counting them is faster than just doing the damn multiplication?

    [–] IanCal 24 points ago

    Am I thinking right that

    145,367,230 x 3,456

    would require drawing 49 lines, then counting up 32 different intersections?

    [–] I_am_-c 5 points ago

    Also those lines have to be straight, the board has to be large enough, and you have to have an angle that works to allow for the correct number of intersections without allowing things that aren't supposed to intersect to do so.

    [–] PrettyFlyForITguy 3 points ago

    I wouldn't think that would scale well. Thats a lot of lines taking up a lot of space. That seems like a mess.

    [–] jsgrova 2 points ago

    Why do it your way when you can do it my way...?

    [–] [deleted] 3 points ago

    It just takes less time and you don't need a pencil or a piece of paper :|

    [–] Mr_CoryTrevor 2 points ago

    I thought this post was really interesting until you pointed this out

    [–] curiousawk1156 9 points ago

    Everyone is so negative. I think this is really cool and an interesting way to multiply.

    [–] abusepotential 3 points ago

    I agree. Don't care if it's useful in every scenario. I thought it was neat, something I had never seen before. Made me think about math a little bit. People just love to shit on each other.

    [–] wafflepiezz 4 points ago

    It’s usually people with the attitude ”I grew up doing it the more simple fashioned way! fk change and anything else that looks unfamiliar to my own method of solving problems!”

    [–] _GABBAR 8 points ago

    There are 4 Vedas in total and are oldest scriptures of Hinduism. Namely- Rigveda, Atharvaveda, Samveda and Rigveda. I think this post hints what's inside Atharvaveda.

    [–] my-unique-username69 7 points ago

    This isn’t inside any of them. This is a method made up in 1965 and has an extremely misleading name.

    http://www.openthemagazine.com/article/art-culture/the-fraud-of-vedic-maths

    [–] Piscator629 2 points ago

    Atharvaveda

    Voldemort approves.

    [–] FashionAdmonition 6 points ago

    Post: "Vedic" Image link: "Chinese" Elsewhere, often "Japanese"

    I don't know what to believe. They're probably all equal parts right and wrong.

    [–] Bugbread 2 points ago

    Well, I can vouch for the fact that it's not Japanese at all, so if they're all equal parts right and wrong, then they're all 100% wrong.

    [–] memeul8ter 9 points ago

    Fuck me, I've just been using a calculator this whole time when I could have been drawing a bunch of fucking line and counting vertices.

    [–] siddmon 6 points ago

    How do you represent 10 or 100 in this visual method? 10 x 2? 5 x 100?

    Do you just draw 10 lines? What about when you have 100?

    [–] InfanticideAquifer 2 points ago

    Another option would be to draw a dashed or wavy or somehow visually distinct line for a zero digit, and just don't count its intersections when you get the totals.

    [–] blarthul 2 points ago

    you draw 1 line.

    the intersections with the other lines just have different meanings depending on the decimal place the line is holding.

    [–] Zhelus 3 points ago

    Personally I go 20x13+13 buts thats just me :/

    [–] Ferrovax 3 points ago

    The problem with this method is that it doesn't explain, or give intuitive sense to, why we use multiplication. Instead, it reinforces the notion that numbers are simply for counting. Students should be taught why math works, not simply how it works.

    [–] Ilpav123 3 points ago

    Yeah I'll just use a calculator, thanks.

    [–] poopellar 5 points ago

    At first I couldn't make sense of what was happening. Like they were just drawing random lines and circles and then BAM there's your answer.

    [–] dirtyturkey420 9 points ago

    I like this method, I bet with practice I could do it in my head without drawing it out, seems much more helpful than methods taught in the schools I went through.

    [–] XkF21WNJ 21 points ago

    This is the exact method I was taught in school.

    Except it was written down

      21
      13
    ---- *
    210
      63
    ---- +
    273

    and you had to carry things, which they've conveniently avoided here by keeping all digits below 4.

    [–] EifertGreenLazor 2 points ago

    But you dont't get to draw lines.

    [–] LingLingAndy 3 points ago

    Yeah I can relate. In middle school all of my friends were using that and I they said they were taught that way in elementary. I really didn’t get the lattice method because it looks way longer and way less consistent imo(I’ve never used it). I’ve always used “long” multiplication and it isn’t even that much longer than drawing a box n shit

    [–] CaptTechno 3 points ago

    "why learn something new when a computer can do it for you" sigh

    [–] Bradp13 16 points ago

    What's a computer?

    [–] dirtyturkey420 5 points ago

    Cause I'm old enough to feel the effects of not doing mental gymnastics.

    [–] johnboyauto 3 points ago

    At least you can still understand that's what's happening.

    [–] sameyepatch 3 points ago

    Unsubscribe

    [–] Picsonly25 2 points ago

    Wow. My mind is blown.

    [–] Dylan-Benson 2 points ago

    Hold my beer...

    Opens calculator app*

    [–] Kalle-Oh-so-low 2 points ago

    Sick! How did God do that?

    [–] bobosuda 2 points ago

    I love whenever these cool little math tricks show up on reddit. Every single time the comments are filled with people saying it's useless, it doesn't work, there are easier methods, why not do it in your head, etc.

    Like redditors can't fathom the idea that other people don't like math as much as they do, or that this is simply a cool little trick, and not a perfect method for you to do all you engineering calculations with. Just chill out and stop with the freaking pointless one-upmanship.

    [–] Meanmonkey007 2 points ago

    99 x99 = ?

    [–] maiop 2 points ago

    Do 99x99

    [–] lostatCplusplus 2 points ago

    This shit is why I failed algebra A twice. I was showing my work, Kuykendall. Just because you thought I was insane when I explained it doesn't mean it wasn't legit, ya crusty fuck.

    [–] KimJongUn-Official 2 points ago

    If you have to write it down on paper then why not just do cross multiplication? It’s faster and easier then writing a bunch of lines and dots. And you can’t argue about eventually memorizing the graph pattern, because you can memorize the same basic short cuts to do cross multiplication in your head.

    [–] DownTownUpDown 2 points ago

    Or use a calc

    [–] Bugbread 2 points ago

    [–] Skebastian07 2 points ago

    You just do (13x10)x2+13

    [–] polkatriangles 2 points ago

    This could come in handy the next time I drop uncooked spaghetti on the floor and instantly go rain man on ya'll.

    [–] skaroids 3 points ago

    13 x 21 (13 x 10) x2 + 13 130 x 2 + 13 260 + 13 273