But I have seen with my own eyes the world record holder Mrs. Lee, when she did less than 10 seconds for such a task. (and 10 tasks in 100 seconds)
Her absolute best for such a task, is around 7 or 8 seconds.

I rarely train such additions, even before competitions.

Abacus and soroban users can be 200% or 300% faster in this category.

Hi Benjamin! You have done a pretty decent job!
I didnāt train for a while, 4 weeks after last time I talked with you, I caught H1N1 flu, and spent a month in hospital, then I was treated for my insomnia and bipolar, I didnāt come home until Nov 7.
But anyway I will still offer some clue. lol
I donāt like to split the numbers when Iām doing Addition in Memoriad, back to August I finished 10 tasks in 190 seconds or so, if I recalled correctly.
Due to lack of training my speed dropped quite a lot, especially when processing big numbers, my grade doing Memoraid Addition now will probably be really, really poor.
So I choose to do 3*3 multiplication, although it is still pretty bad and within 1 error, but at least not that heartbreaking. lol Iām so sorry

When I realized that there are other advanced methods like soroban or criss cross, It was a little bit too late, and Iām not willing to adopt a new system, since vertical method works well for me.

Thatās pretty good Benjamin, you are getting really fast. I havenāt done any addition in a long time, Iāve never done that type of addition either. I guess I have to check out Memoriad.

Can you explain how you do it? Because Iāve been trying to find some videos about vertical method (Iāve never learned it, they didnāt teach us that at school) but canāt find one with large multiplications, only 2 by 2 and 3 by 2.

In every video Iāve come across of vertical method they go from right to left but you go from left to right.

When I calculate 338x886 I need to calculate 300x886+30Ć886 first and then I know that the first digit is a 2 but you know instantly, in less than a second that the first digit is 2, how?

How can you calculate 330Ć886 in less than a second but then take 2-4 more seconds to calculate 8x886?

I canāt find a video that explains your way of calculating, could you please explain it? I think I am missing something obvious but I donāt know what.

Itās doesnāt really matter whether from left or right to start. Just little change can tackle this problem.

Itās tidy for people who calculate by pen. But for mental calculation using vertical method, i think itās better (at least for me) to write it from left to right, the advantages it brings are more than disadvantages.

I think this picture could tell you something.
In an n*n multiplication(here we only consider about the 2n answer, no 2n-1), the first digits is easy to determine(sometimes need to estimate, whether +1 or not) and the second digits to the n-1th digits is the most difficult part, and the n+1th digits to 2nth digits are follow by the nth digit.
(Wish you could understand what I mean. My English donāt allow me to explain complex concept. )

Itās 330x886 and 038x886.
My speed is constant(approximately), most of the time it wonāt vary dramatically.
2-4 seconds more seconds is a little bit too long. Most of the time I donāt even need that long to finish the task, including the time writing it done.

Itās an simple method. I think you would gradually understand after you start using it!

I still donāt understand. The reason the cross method is so populair is because it is essentially single digit multiplications and adding the answers up. For example, 215Ć347 is (2Ć3)+(2Ć4+3Ć1)+(2Ć7+3Ć5+1Ć4)+(1Ć7+4Ć5)+(7Ć5), which is much easier than the basic method from elementary school. With the cross method you can calculate the first digit instantly too because you have to deal with very small calculations like 2x3 and 2x4+3x1.

I have to calculate 200x347= 69,400, 10x347=3470, 5x347= 1735.

I cannot instantly know the first digit because I cannot calculate 200x347 and 10x347 and then add up 69,400 + 3470 that fast, I need 1-2 seconds.

How do you determine the first digit of 478x896? That is what I need to know.

Calculate the 478x8, and the first digit is obvious. (Whether +1 or not depends on 478x9, if didnāt +1 just delete the first digits and +1, and so on.) Thatās how it work.

I 'm a little tired of answering this type of questions, I think you can figure them out yourself later.

I am actually terrible at doing additions like these ones fast haha, I took around 100s average on all 10. While I love math and finding ways to do it easier, I am not good at doing it speeding it up

Ah, I understand. You calculate 478x8=3824, I calculate 478x800=382,400. To me 3824 is completely different from 382,400. I never learned to carry over digits and leave out zeroās. I remember other kids at my school using this method, I didnāt understand what they were doing back then. I do now. My girlfriend used the vertical method too in school, she said it is sort of a short cut and easier than the basic method, the basic method is what I do. I guess I am too used to the basic method because the vertical method is too strange for me to do, without the zeroās I get confused.