38 + 85 by Finger Maths?

I would like to know how to do additions by using “Finger Maths” method.

Thanks in advance for your help.

Just like you would on a soroban…

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I´m calculating 349 + 7

In my left hand I have all my fingers occupied except my thumb.

In my right hand I have all my fingers occupied.

Now I add 7 in the left hand. I start by raising the thumb of the right hand and raising the thumb of the left hand, because every time I raise the thumb of the right hand I have to raise the thumb of the left hand, right? Well, it gives me 350.

Then I turn my right hand again, reaching his thumb and raising the thumb of the other hand, the left. It gives me 365.

I finally lift the index finger of my right hand and it gives me 366.

But here is a mistake, I don’t know which one.

Okay, that’s a 4 and a 9 for a 49…

Why? You want to add 7 not 70.

How? It’s already raised…

You already asked how to do soroban addition here. Just follow the steps that @Kinma was showing you there, but use your fingers as described above.

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Sorry I means the right hand…

But in Soroban you have complementary number rules, it’s a world in itself, an hard one.

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This is another video explaining how to calculate with the finger method.

Like moving beads on the soroban you use five’s complement.
Example. Let’s look at the right hand and put 4 on the fingers.
Now add 4. You cannot put 8 fingers down so you need to use the 5’s complement of 4 or 1.
So subtract one from the 4 fingers down, making it 3 fingers down and put the thumb down for adding 5. => 4+4 = 8.

In short if you can put more fingers (excluding thumb) down, you do. 2+2 = 4.
If you cannot, use the five’s complement.4+4 = 3 fingers + 1 thumb.
If the thumb is already down; involve the thumb on your left hand. 8+3. Here is the process.
8 = 3 fingers + 1 thumb. Now add 3. 3 fingers down means we need to use 5’s complement. 5’s complement of 3 is 2. Subtract 2 from 3 fingers down.The fingers change from 3 down to 1 down.
Now involve the thumb. It has only 2 positions; up and down. Since it is down it moves to up (no thinking involved it you get the hang of this). Since it moves from down to up we need to add one on the left side.
End result: one down left and one down right or 11.

If you can do this with some (moderate) amount of speed, you can add shortcuts, like adding 5 to 8 is only moving one on the left and the thumb on the right. This is the same as moving 2 beads at the same time on the soroban (in the same calculation).

Here is the training you need to do in order to get the speed down.
After each repetition, say the end result in your head and feel your fingers’ position.

1: Put 0 on your fingers and add 1 repetitiously. do this until you reach 100.

2: Put 0 on your fingers and add 2 repetitiously. do this until you reach 200.
3: Put 1 on your fingers and add 2 repetitiously. do this until you reach 200.

4: Put 0 on your fingers and add 3 repetitiously. do this until you reach 300.
5: Put 1 on your fingers and add 3 repetitiously. do this until you reach 300.
6: Put 2 on your fingers and add 3 repetitiously. do this until you reach 300.

7: Put 0 on your fingers and add 4 repetitiously. do this until you reach 400.
8: Put 1 on your fingers and add 4 repetitiously. do this until you reach 400.
9: Put 2 on your fingers and add 4 repetitiously. do this until you reach 400.
10: Put 3 on your fingers and add 4 repetitiously. do this until you reach 400.

11: Put 0 on your fingers and add 5 repetitiously. do this until you reach 500.
12: Put 1 on your fingers and add 5 repetitiously. do this until you reach 500.
13: Put 2 on your fingers and add 5 repetitiously. do this until you reach 500.
14: Put 3 on your fingers and add 5 repetitiously. do this until you reach 500.
15: Put 4 on your fingers and add 5 repetitiously. do this until you reach 500.

etc., etc.

Each step consist of a hundred moves. You can do less. However; do at least more than 20 or so.

Do this for a week (every day several hours) and you can think of two numbers to add and then your fingers will move without you thinking about it.

If not; repeat.

IF
YOU
WANT
TO
DO
THIS
FAST you HAVE to put in
THE
WORK
AND
THE
HOURS!

@benjamin1990
Why am I saying this?
In half a year you asked about logarithms, multiplications, additions and more.

Tell me about your progress, please.
How many hours do you put into mental calculation a week?
My feeling is that you dabble in this, but you do not have a training schedule or a plan in order to get better.

You always ask ‘what is the best’? And you cannot make that decision yourself for lack of experience. My answer is invariably ‘try both and see what works best for you’.
You are measuring yourself against the worlds best in a field.
You see finger counting, it blows your mind and you want to be able to do this too.

The best in the field can only do this after years and years of training.
Same with Maria Lizeth Duarte. Although she is only 14 years old, she was winning prices from when she was 12. Which means at the age of 12 she had already put in many, many hours.

You have to do the work, spend hours and hours on doing this (while your friends party).

Personally, I know a lot of techniques. However; I cannot measure myself against the worlds’ fastest mental calculators. I am fast, just nowhere fast enough!

I don’t need to be that fast though. I meetings I can do calculations faster than 99% of my colleagues because in the time they fetch their phones I have already made an estimate.
An I can also do this because I know so many different ways of calculating that I can usually fetch just the one that is fast.

Also; read this:
https://www.ee.ryerson.ca/~elf/abacus/feynman.html

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First of all, THANKS FOR YOUR HELP.

I have understand now how to do Finger Math [at least!, and is amazing how we humans have alls a natural soroban in our hands] and I have made 4-5 exercices of 2 digits to corroborate it.

For example, to do 53 + 89 I put I lift my left thumb (it gives me 50) and lift three fingers on my right hand, the first three minus the thumb. Then I have 53.

Now I add 80, which is to subtract my thumb 20. 50 - 20 = 30, then I already have 130 + 3 = 133.

Then I add the 9 in the right hand. For this, as in the soroban, I subtract 1 to the three fingers of the right hand and it gives me 2.

As in total I have added a tens in the left hand, so it gives me 130 + 10 = 140

140 in the left hand and 2 in the right hand, then gives me 142 as the final result.

Then, you ask me about my progressions. Unfortunately I do not have the time I would like to improve in the calculation available, and that is why I always ask what is the best technique to move forward.

At the most I have 15 minutes a day for the calculation, having problems studying and trying to get my Geography degree

By the way, I love your advice and I appreciate you. I will try to add 5 more minutes to do 20 minutes or 30 minutes.

I find it hard to get the race and I also practice sports. But I want to be good in this field because I like it.

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You are welcome!

The best technique IMHO as you know by now is to know them all.

My last calculation is 49 X 81.
I could have done the criss-cross, but in this case and for me the following steps give me an answer much quicker:
Half 81 and add a zero: 4050. Then subtract 81.
Done.

So try each and every method you can find, ask questions. If you cannot find answers, ask them here.

I understand you need time to study for your degree.
Just use the numbers you see IRL.
If you call a friend, use 4 digits from the telephone number to do a quick 2x2 multiplication for example. Then take another 2 digits and get the logarithm. Both base 10 and base e.
Etc.

ABC - always be calculating :slight_smile:

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