I was surprised when I came across with an article on Polish hand magic, a strategy for multiplication using fingers. I remember us doing it when we were in the first grade, but in a slightly different way. Here in our country, we call it Finger Math or Finger Multiplication.
Finger multiplication is a strategy for multiplying numbers from 6 to 10. It is used by pupils in the early grades who have not memorized the multiplication table yet. The idea is to assign the numbers from 6 to 10 to each finger on both hands (see Figure 1): 6 to the pinkie, 7 to the ring finger, 8 to the middle finger, 9 to the index finger, and 10 to the thumb.
To multiply, do the following (see Figure 2):
(1) Connect the fingers assigned to the numbers that you want to multiply. For example, in multiplying 8 and 7, connect the middle finger and the ring finger (see Figure 2).
(2) Next, we count by 10s the connected finger and all the fingers below them, then find their sum. In the figure, we have 50.
(3) Next, count the fingers above the connected fingers and multiply the number of fingers on the left hand to the number of fingers on the right hand. In the second figure, we have 2 x 3 = 6.
(4) Add the sum obtained in (2) and the product obtained in (3): 50 + 6 = 56.
In the second example (see Figure 3), we multiply 7 and 9. We do this by connecting the index finger and the ring finger. Again, we count by 10s the connected fingers below and all the fingers below them. This gives us 60. Next, we count by 1 the fingers above the connected fingers and multiply the number of fingers the left by the number of fingers at the right which 3 x 1 = 3. We add up: 60 + 3 = 63.
Now, try multiplying the following if it works: (1) 8 and 6, (2) 9 and 6, and (3) 10 and 0.
In the next post, you will be more amazed when we discuss why the strategy above works.
Photo Credit: Mi Mano vy Vimayr