Jeonghee Lee on Russian Show. So impressive


Did she memorize all numbers? The microchip is working.

Shes Korean and the show is in Russia. She doesn’t speak Russian. She use a translator.

It does not appear that she memorized since she is a human calculator and not a memory person. From the looks of it, the task seems to add all the very long numbers, half of which are written upside down, but someone with knowledge of Russian may confirm


Jeonghee Lee is the world record holder for Addition, Division and in 2018 was briefly the fastest for Multiplication too. She’s a soroban teacher in New York, and has been doing mental calculation for decades.

I’ve met her a couple of times in competitions, and she can add up to 10 digits per second with very high accuracy. For sure she is doing this by calculation rather than memory.

For additions she usually calculates 3 columns at once, starting from the rightmost 3 columns. Last year I had an interview with her here if you want to learn more about her.

I also recognized the stage of that program as Wenzel Grüß (another calculation prodigy) has been on that show performing Köpfball (link to YouTube) where he heads a ball while performing multiplications.


Why she split the numbers? Wouldn’t it be faster if she calculate it in a row?

It’s only possible to keep a few digits in your head at once (whether you’re using your inner monologue, imagining numbers, imagining soroban beads, etc.) so any method for addition needs to work around that limitation.

Jeonghee Lee can keep 5-6 digits in her head at once while operating at full speed, so she chooses to work in columns of widths 3 or 4.

I visualize the numbers and silent read it. Currently I can calculate 22 digits in my head and I’m still trying to extend it longer. My full speed is just around 10 digits. I also split the numbers in my head,e.g. I split 10 digits numbers into two five digits, but I would rather not write it down. If they don’t keep 10 digits or more numbers at once, then how could they process 8 8 mulitiplication and do it that fast? It takes me 16 numbers working memory to process 8 8.

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Top calculators use the cross-multiplication method (Freddis Reyes, Marc Jornet Sanz, most Indians) or an equivalent version (Jeonghee Lee).

This means that you only need to keep 4-5 digits in your working memory at a time (a 1- to 3-digit running total, and a 1x1 multiplication).

Here’s an explanation of the cross-multiplication method for mental multiplication.

Without this method, it becomes very slow if both of the numbers to multiply are longer than 3 digits.

I’m a little shocked.I have never learned of this method.Its name is similar to a method I have learned. I’m now using the vertical method which every Chinese students study in primary school.Its format is like that:


9801 Which differs is that I do it in my head. It’s may not be the easiest way, but the simplest i think. I didn’t face the problem you mentioned, but maybe I will try cross-multiplication method somedays.

The format become a little messy due to the typesetting mechanism. But you might already known that method. I will give some explanation if my presentation is incomprehensible.

I’ve being training for five months, and recently my insomnia became much severe than ever. I lose sleep all night 3 days in a week, and the quality and quantity also dropped sharply in the days I could sleep. I get nervous during the night. The day before I tested my 5*5 but only scored 225 sec within three error. I doubt if I could maintain my grade if my insomnia last for a long time. I wonder how you adjust your mindset and do you ever had insomnia? If yes how did you conquer it?Thanks.

According to data from I notice that Granth Thakkar could do 10 sets of 88 multiplcation in under 307sec. But I also found he is still the record holder of 2020 multiplication, which is only under 168 sec. I wonder how could he do 20*20 that efficiently. There is very little information about him.

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For insomnia, I recommend that soon before sleeping you do 10 minutes of basic meditation to calm the mind, followed by a few minutes of the 4-7-8 breathing technique to calm the parasympathetic nervous system.

I have always had problems with insomnia too, and this has helped me :slight_smile:

For Granth Thakkar, maybe he got lucky with an easy question for the 20-by-20 multiplication, and/or hasn’t had many record attempts with the 8-by-8 multiplication.

I would expect a 20-by-20 multiplication to take about 7x longer than an 8-by-8 multiplication, in general.

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Thanks for your reply!

How did you test this? 20 digits in 0.5 seconds is an extraordinary claim.

An app downloaded from app store China,which is called ‘速記數字’ in Chinese. You can adjust speed(0.4 sec-5 sec) and digits (1-20) in the settings.

20 digits in 0.5 seconds would make you faster than the best memory champions in the world right now. Could you demonstrate it on ?

It would be really impressive if this feat is real.

Hi albinoblanke, the splitting of number in is quite annoying. I’d like to memorize it without splitting.
The best memory champion is definitely faster than me. My speed card only scored 48 sec right now.

I also find it annoying, I have synesthesia and the splitting works against me a lot. I’ve already send a message a while ago to memory league about this, they will try to change it. Could you perhaps demonstrate it with another program?

Maybe in cards but your claim of 20 digits in 0.5 second crushes any world champion in numbers. You should be able to memorize 80 digits in 10 seconds or way less if your feat is real.