Multiplying by 9
I found this out recently and checked to see if anyone else had discovered this but I don't think so. I found a simple way to multiply any number by 9.
Summer of Math Exposition
Presented by 
3blue1brown
Presented by 3blue1brown
I found this out recently and checked to see if anyone else had discovered this but I don't think so. I found a simple way to multiply any number by 9.