Multiplication using lines

To make this work you have to draw the lines so my equation is 21x42. What I do is I draw 2 lines then leave a space then I draw 1 line. That makes 21. Then I draw 4 lines going the other direction then leave a space and then draw 2 lines. Now we draw curved lines to separate the numbers. Now lets count the first dots. I counted 8 dots then the middle ones, I counted 8 dots and the last ones I counted 2 dots. Put it together and you get 21x42=882√

Hope you learnt a new trick!