Hello everyone!
I am new to this website, and I am learning the soroban for nearly a month now.
The way I do division about problems with divisors having more than 2 digits is called modoshizan （戻し算）, which means "returning number" calculation. I only know the multiplication table from ones to tens.
From my own understanding, basically it goes like this:
84 / 28
(I stole this from a Japanese YouTube video lol)
- Quotient answer is at the ones place.
- Divide 8 from 84 by 2 to get 4; 4*2=8, and subtract the leftmost digit of the dividend by 80 to get 04.
- Focusing on the second digit of the divisor, 8 (from 28) * 4 (from quotient) = 32. But we cannot subtract because 32 is greater than 4 (from the divisor).
- We do this by taking one away from the quotient, hence the name. And add 20 from 28 to the dividend, now it is 24.
- Again, 8*3 = 24 and the dividend is 24, subtract it by 24 to get 0.
- The process is done because we went through all digits of the divisor, and the answer is 3.
(This explanation took way too long, so apologies if I missed a crucial step.)
What I want for the virtual soroban is showing how modoshizan calculations are done step-by-step. For the 'division' tutorial, it isn't really helpful if it only tells me which quotients I should choose.
How can I tell if 3 is the quotient from 84 and 23 if it is out of range from my multiplication table?
It would be helpful to know how it would calculate 720 / 15 because that equation stumped me from doing it. All I know is that would require me memorizing the multiplication table of fifteens.
Thank you for your time reading this forum post suggestion.
:)
Hello arik,
What I understand is that you are using a clever method (modoshizan ?), that allows you to adjust the quotient you choose when you are doing a division.
In your example 84/28, say you choose a quotient of 4, that is too big; instead of resetting your operation, and doing costly changes and possibly messing your operation, you adjust the quotient.
What I found online, is that you do it like that:
If your quotient is too high, you decrease it by 1, then you count 2 rows to the right of that quotient, and then add on the selected row the amount of the digit divisor you are using.
And you can repeat the process multiple times, until you reach the correct amount for the quotient.
This is a method to be used if you don't find right away, the correct quotient, by backtracking if one can say.
But, in fact, you are using the main method of doing the division. In between each step, you add steps to adjust the quotient, if you made the wrong guess. that's all ;-)
What I show on the virtual soroban, is the ideal way to make a division, with the correct quotient, right away.
I can't add all the way to adjust a quotient like that, because you can use many different quotients sometimes; so this leads to too many possibilities to be displayed.
You can get the steps to do the division 720/15 by using the custom operation on the tutorial page of the virtual soroban.
You don't need to learn the 15 multiplication table, because for a 2 digit divisor, you take each digit 1 then 5 separately
Go to https://www.sorobanexam.org/tutorials.ht... and in the "Custom operation" input box, type in "720/15", and press play, to watch the steps on the virtual soroban.
This should help you understand how to do it