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Discussion Starter #1
1. Grab a calculator. (you won't be able to do this one in your head)

2. Key in the first three digits of your phone number (NOT the area code)

3. Multiply by 80

4. Add 1

5. Multiply by 250

6. Add the last 4 digits of your phone number

7. Add the last 4 digits of your phone number again.

8. Subtract 250

9. Divide number by 2
 

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Vince, that's clever but how am I supposed to get any work done?!

Now to ruin the fun ;) (sorry for the ugly display, software won't let me center the 2, keeps left justifying it)

The steps followed can be expressed mathematically as (where x is the prefix and y is the last four digits):

250(80x + 1) + 2y -250
2

Simplified this becomes:

20000x + 250 + 2y - 250

2

The 250's cancel each other out, leaving:

20000x + 2y
2

Dividing by 2 is how you get your phone #:
10000x + y

Simple, but nonetheless clever reverse engineering by the author :).
 
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