How to subtract natural numbers using pencil and paper
If you managed somehow into this most peculiar situation sitting with two numbers on your hands and have no idea what to do with them, here is the answer: among the number of things you may chose to do with the numbers you can subtract one from another.
Of course, you're equipped with your modern multigigahertz computing power and have a number of handheld calculators lying around, but you have no time machine on your desk, do you? And if you don't, then you may have no idea that there is a magic we used to use in the ancient times of paper and pencil arithmetics.
The secrets of past revealed! You can see the trick with your own eyes now!
Just enter two natural numbers and click the '=' button