The Chisanbop is a Korean method of counting with hands that allows you to arrive up to 99 and easily perform mental calculations. It was invented around 1940 and is structured as follows:
- there right hand represents the units: the thumb it’s worth it 5While the other fingers they are worth each one 1;
- there left hand represents the tens: the thumb it’s worth it 50While the other fingers they are worth each one 10.
To dial numbers, all you need to do is press your fingers on the table. In the image below, for example, the number 36. In fact, three fingers of the left hand are pressed, therefore 10 + 10 + 10 = 30, and the thumb and index finger of the right hand, therefore 5 + 1 = 6, for a total of 30 + 6 = 36.
Thanks to this way of counting, with the fingers of two hands we can reach up to 99 if all the fingers of both hands are pressed on the table.
The Chisanbop method is very useful for quickly performing addition. In fact, all you need to do is – like when we count in decimals – add more fingers to the count to get to the desired result. If for example we want add 11 to 21we can first compose 11 by pressing a finger of the left hand and a finger of the right hand on the table, and then add 21 by pressing two more fingers of the left hand and another finger of the right hand on the table. The result will be to have three fingers of the left hand and two fingers of the right hand pressed together, for a total of 32, which is precisely the result of 11 + 21.
Things get a little more complicated when the result has tens or ones greater than 50 or 5, because the inch comes into play. If we want in fact perform the operation 34 + 47what we have to do is first dial the number 34 by pressing three fingers of the left hand and four of the right hand on the table.
Let’s now represent the number 47 with the remaining fingers. Starting from the units, on the right hand we must obtain 4 + 7 = 11. To do this, we remove the two fingers that we had previously pressed and press only one finger of the left hand on the table, while on the right hand we press one finger to obtain 10. At this point, on the left hand we have the 3 fingers previously pressed for 30, plus a finger obtained from the sum of the units. We are therefore at 40.
So let’s focus on the decisions of our addend. We need to add another 40, thus obtaining 40 + 40 = 80. To do this, we just need to raise the fingers of the left hand that we had previously pressed and press the thumb and three fingers, so as to obtain 50 + 30 = 80.
At this point, we have 80 on the left hand and 1 on the right hand, for a total of 81, which is just 34 + 47.
