Originally posted by zebano
Neat trick, totally impractical. I just wonder how many people can prove why it works*.
*should be trivial if you know how multiplication works (I too am a skeptic).
Using marbles, I can represent 3*2 as 3 groups of two marbles each. The trick on the video simply substitutes line intersections for marbles. The lines are all drawn diagonally to keep the proper order of magnitude for each number.
However, try the intersection trick for 9*9, and you will see why we use times tables instead.