Multiplication of two numbers is easy, right? At primary school we learn how to do long multiplication like this: Methods similar to this go back thousands of years, at least to the ancient Sumerians ...

What are you like at multiplications? Chances are if you're a mere mortal 2, 5s and 10s won't seem too taxing. But when it comes to figuring out what 42x21 is, you may wish somebody had shown you the ...