Note: You can click and drag the numbers up and down to change what you're multiplying.

Cracker Multiplication

May 2022

Cracker Multiplication is a program that visualizes long multiplication using the holes in a cracker. It splits the width and height of the cracker by the ones and tens place.

For example, in the above graphic, 12 * 15 is split into (10 + 2) * (10 + 5)

This shows how the standard Western method of doing long multiplication works: it's just a way to break down the problem (like 12 * 15) into smaller problems (like 10 * 10, 10 * 2, 10 * 5, and 2 * 5) that you can solve if you know your times tables, and summing up the results.

Inspiration

When I learned long multiplication in school, I was taught how to do it, but I didn't understand why the method works the way it does. I thought it was confusing, and for years, I kept forgetting how to do it, because I didn't understand it.

So the idea with Cracker Multiplication is to visually explain why long multiplication works the way it does, to make it easier to understand and more memorable.

However, some cultures teach other ways to do long multiplication, like this one from Japan. It might look a little bit confusing at first, but it's actually very straightforward:

It even works for numbers with more than two digits:

Maybe the Japanese method gives students a better understanding of the way that long multiplication breaks down a problem by digit places.