I love math. I love math tricks, especially ones that are a lot more complicated than they should be.
Here's one I found the other day.
Take any two numbers from 1-9.
Multiply the first number by 5.
Double the number.
Add second number.
And wa la. You have a number with your two numbers as its digits.
In algebra this expression would look like this:
So, it's not magic after all.