This is a simple way to multiply (from 1 to 10) by 9. We should consider the fingers counting from left to right and numbering them sequentially from 1 to 10. So, just lower the finger corresponding to the number we want to multiply by 9, and we will have the result.
For example: 4x9. We lowered the finger corresponding to number 4. Note that there were 3 fingers on the left side and 6 fingers on the right side of the lowered finger. Now just join the 3 and 6, that is, the result is 36.* Submitted by user Alessandro Fonseca de Araújo