In the Finger Multiplication post, we have learned how we can cleverly multiply numbers from 6 to 10 using our fingers without memorizing the multiplication table. In this post, we will discuss the reason why this method works. The proof can be written in a few lines, but since this article falls under the elementary school mathematics category, we will discuss it with more details.
Let’s examine the first example in the previous article as shown above. In the example, we wanted to multiply 8 by 7, so we connected the ring and the middle fingers. In this discussion, we will call the connected fingers and all the fingers below them down fingers, while we call all the fingers above them up fingers. » Read more