I still remember being surprised to hear that multiplication tables are memorized up to 99×99 in India. Actually, it seems to be different depending on the area, and it seems that there are many places to remember up to 20 × 20, but it is still surprising.
Nowadays, multiplication of many digits can be easily calculated with a smartphone, so it seems that there is not much merit, but that is not the case.
In India, a method of easy multiplication is also handed down. As expected, it is the country that discovered zero. With these techniques, you can mentally calculate 2-digit multiplication by just remembering multiplication tables up to 9×9. (Or you can easily calculate by writing a few notes.)
Mental arithmetic of 2-digit multiplication with these methods is a good brain training for the memory area and calculation area of the brain.
The Android app “2Digit Multiplication” contains many methods for 2-digit multiplication.
Here, I will mainly introduce the Android app “2Digit Multiplication”.
◆Android app ‘2Digit Multiplication’ free version and paid version
There are a paid version of “2Digit Multiplication” and a free version of “2Digit Multiplication Free” as Android apps that include 2-digit multiplication methods.
“2Digit Multiplication” contains 15 methods (G A1 A2 A3 A4 A5 A6 B1 B2 C1 C2 D1 D2 D3 D4).
“2 Digit Multiplication Free” contains three methods (G A1 A2).
For multiplications up to 19×19, you can do mental arithmetic just by learning Method A1.
◆How to use the Android app “2Digit Multiplication”
Usage is the same for mobile phones and tablets. Here I’ll use the screenshots of the tablet.
Tap the play button at the right end of the method row you want to learn.
The “1/3” displayed at the bottom indicates that it is the first of the three steps. Tap the play button on the right side to advance the step, and tap the back button on the left side to move the step back.
Calculate the problem displayed under the play button in the method row.
Check the answer by tapping the play button.
When you return from the answer screen (method description screen), the questions displayed under the play button will change randomly.
Android apps “2Digit Multiplication” and “2Digit Multiplication Free” can be downloaded from Google Play.