This one's from Peggy. She said to use a calculator, because you won't be able to do it in your head. Though I'm sure some of you can.
1) Key in the first three digits of your phone number (not the area code).
3) Add 1.
4) Multiply by 250.
5) Add the last four digits of your phone number.
6) Add the last four digits of your phone number again.
7) Subtract 250.
8) Divide by 2.
This is how you do it. Let your phone number be abc-defg (this is easier than substituting real numbers and having to do all the math), then the equation is:
[250X[(abcX80)+1] ]+2 defg-250
20000Xabc + 250 + 2 defg - 250
10000 abc + 125 + defg - 125
abc0000 + defg. If you replace the digits with any numbers, it is obvious that the "0000" are just place holders, and when you add the two together, you get
abc,defg, or the phone number you started with in the first place.
[Image via DHD multimedia gallery]