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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!

For example:

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.

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