A fun fact from Perry, the wannabe mathematician:
If a is a positive, whole number (written in base ten*) and b is a new number created by rearranging the digits in your original number (a), then a – b is always divisible by 9!
a = 3829174 and b = 8237419 then a – b = -4408245
Is a – b = -4408245 divisible by 9? Let’s plug it in a calculator and find out!
-4408245/9 = -489805 … so, yes, it is divisible by 9!
(If you test this out, don’t forget that 0 is divisible by 9).
*This means that you would write it like you would normally write a number. I’ve specified this, however, for any nitpickers out there.