Back in primary school when we were learning how to multiply two, multi-digit numbers by hand, our teacher showed us a little trick to verify that we had the correct result calculated. I was impressed ...

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 ...