Recreational Mathematics

[xoxoxoBruce]

Hmm

[xoxoxoBruce]

and

[ZenGum]

Japanese multiplication method

The lines and numbers above may not make any sense at first, but according to William C. at Themetapicture.com: "The lines over the circles are color coded. notice the single red line and 3 blue lines representing "13" group together while the single green and 2 black lines take their own group. [Simply] draw your first group of lines in one direction then your second group of lines going over the first, count the groups of intersections and there's your answer."

ETA:

[Lamplighter]

[quote=ZenGum;847990]Japanese multiplication method


Attachment 42457

This is an interesting illustration.
But I doubt adults use the the method.
It's sort of like kids adding by counting on their fingers.
It's also what we do in algebric multiplication of polynomials...




but then if, as Big V asks, what happens with zero's, we leave gaps in the summation: