To multiply two numbers by hand takes a few steps but it's something we're taught in school. When dealing with big numbers, really big numbers, we need to a quicker way to do things.

To help you understand the algorithm, the video shows a simple two-digit by two-digit multiplication. You can see that the first and last digits are essentially the result of one multiplication.

The Common Core State Standards teach students the algorithm for multi-digit addition and subtraction in 4th grade. But some experts say it should be taught sooner.