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.

We'll explore how this shortcut works for both two-digit numbers multiplied by themselves, and even for multiplying two different numbers ending in 5.

Multiplication of two numbers is easy, right? At primary school we learn how to do long multiplication like this: The long way to multiplication. David Harvey Methods similar to this go back thousands ...

Multiplying 2 x 2 is easy. But multiplying two numbers with more than a billion digits each — that takes some serious computation. The multiplication technique taught in grade school may be ...