Always End With 1089

Add two numbers together and always end with 1089.

Here is How:

Pick a three digit number. The three numbers used must be different*. i.e. 123
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Reverse that number. 123 becomes 321

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Take the smallest three digit number from the largest.
321 − 123 = 198
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Take the answer and reverse that number. 198 becomes 891

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Add that number to the answer of the subtraction.
891 + 198 = 1089
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The answer will be 1089!

So why does it do this?
Find out here



A Little Footnote

But I ended with 198 not 1089 ... !

This happens if you pick a number like 546.

546 goes like this: 645−546=99, then 99+99=198.

BUT if you assume that 099 is a 3 digit number, you will get:
990−099=891, and 891+198=1089

*If you don't pick three different numbers then this might happen:
343−343=0, 0+0=0